SQT - Stupid Questions Thread

>>7980526
type that shit in wolfram alpha
noone's gonna do that baby shit for you, kid.

Currently at a community college taking an 8 week course on History. It's busy work and complete garbage. It's too late for me since I am already taking the course, but how do we get rid of this requirement for future generations?

>>7980526
Are you a retard?
[math]e^{ix}=e^{ix+0}=e^{ix+i\frac{y}{2}-i\frac{y}{2}}[/math]

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>>7980526
>OP can't into adding 0

I want to get the Fourier transform w.r.t. position of the many body Green's function
[math]G\left(\mathbf{x},t;\mathbf{x}',t'\right)= -i \langle T\left[ \Psi \left(\mathbf{x},t\right) \Psi^{\dagger}\left(\mathbf{x}',t'\right)\right]\rangle[\math]
where the psis denote the field operators in Heisenberg representation.

I know that for a homogeneous system (i.e. momentum is conserved) I should find something like
[math]G\left(\mathbf{p};t,t'\right)= -i \langle T\left[ a_{\mathbf{p}}\left(t\right) a^{\dagger}_{\mathbf{p}}\left(t'\right)\right]\rangle[\math]
However I can't figure out how to get there. Can (m)Anybody help?

>>7980751
[math] G\left(\mathbf{x},t;\mathbf{x}',t'\right)= -i \langle T\left[ \Psi \left(\mathbf{x},t\right) \Psi^{\dagger}\left(\mathbf{x}',t'\right)\right]\rangle [\math]

[math] G\left(\mathbf{p};t,t'\right)= -i \langle T\left[ a_{\mathbf{p}}\left(t\right) a^{\dagger}_{\mathbf{p}}\left(t'\right)\right]\rangle [\math]

>>7980753
what am I doing wrong?

[math] G\left(\mathbf{x},t;\mathbf{x}',t'\right)= -i \langle T\left[ \Psi \left(\mathbf{x},t\right) \Psi^{\dagger}\left(\mathbf{x}',t'\right)\right]\rangle [/math]

[math] G\left(\mathbf{p};t,t'\right)= -i \langle T\left[ a_{\mathbf{p}}\left(t\right) a^{\dagger}_{\mathbf{p}}\left(t'\right)\right]\rangle [/math]

What does a box plot with boxes of equal length and one short whisker (to the right) and one long whisker indicate?

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>>7980751
>>7980759
Express [math] \Phi(x) [/math] as k-integral over [math]a_k[/math]'s. Look it up, it'll introduce integrands <x|p> = exp(-ikx), while the Fouirer transform also introduces exp(-ipx)'s) and use some representation of the Dirac delta to get rid of one of the integrals. Might be that you have to permute some operators and use a|0>=0.

---

Not a stupid question, but something cool I learned today (and it vaguely relates to path integrals, but that just as an aside):

If for some n you consider a list of numbers
[math] r = (r_1, r_2, ..., r_m) [/math]
with elements randomly taken from some interval [math] [-d, d] [/math], then you have a good chance that [math] \sum_i r_i [/math] is close to zero, because the number cancel their values (on the real line).
Take instead numbers from [math] [0, d] [/math] and assign complex phases
[math] r_i \mapsto r_i \, \exp( i \, \alpha_i )[/math]
to them, and the same still holds (not on the complex plane).
If however, you were to assign a weight with absolute value bigger than one, e.g.
[math] r_i \mapsto r_i \, 7^i \, \exp( i \, \alpha_i )[/math]
Then the terms with n very high would dominate the sum and you surely would not end up with a sum close to zero.

As a result of this, if you take a random polynomial [math] p(z) = \sum_{i=0}^n r_n z^n [/math] of high order, their complex roots ([math] z_k [/math] so that [math] p(z_k) = 0 [/math]) will all align close to the complex unit circle.

http://mathoverflow.net/questions/182412/why-do-roots-of-polynomials-tend-to-have-absolute-value-close-to-1

---

Another thing, I stumbled upon a github page where someone has collected the bibliography of Per Martin "Intuitionistic Type Theory" Löf
https://github.com/michaelt/martin-lof

Besides the type- and complexity theory papers, relevant to some of the recent threads here, 25 years ago he wrote a paper
>Mathematics of Infinity
and there is another interesting one
>Hilbert Brouwer Controversy Resolved?

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Would this boxplot still be considered right-skewed? My textbook states that for a boxplot to left or right skewed, either a left or right whisker plus one side of a box has to be longer than the other.

Which clearly is not the case in the pic, though the left whisker is longer, while the right is shorter. The data does appear to be located around the higher values.

>>7980961
It's counter intuitive but that dataset is left skewed

>>7980883
i did that, for each of the psis I get one momentum integral (say p and q) but because they come with factors exp(ipx) and exp(-iqx') I can't make the Dirac delta identity work.

I need to make use of momentum conservation somehow, because otherwise this does not hold, but simply setting p=q by hand feels wrong...

>>7980993

Ignore this. I've just realised my mistake.

So the data is still considered left skewed despite the two boxes being the same length?

I am majoring in computer engineering in the fall of 2016. What should a brush up on to get ready and succeed in my computer engineering courses?

>>7980980

So the data is still considered left skewed despite the two boxes being the same length?

>>7981034
There is only one box, and it's position defines the skewness not it's length

lurk more

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>>7981057

I'm referring to the two parts of the box from where it's split. No need to be a jackass.

My textbook states that, both a whisker and a portion of the box, have to be longer on one side to be considered skewed. As you can see in the pic.

>>7981028
In the end result, x is clearly integrated out
Protip: start working out and do the obvious steps instead of doing nothing and wondering.

How do i get access to a lab to develop muh shitty ideas.

Can I take classes for engineering as a computer science major?

I may be accepted into a great school as a CS major because I lack a course requisite in time for engineering

I'm an american and will be taking calculus 1 in the summer, the prerequisite for engineering is at least cal 2

This means if I attend the school for CS I'll have to wait until I have about 27-30 credits before major transferral

I'm a freshman now, to be a sophomore.

I can go to another school with an engineering major already, however this other school is literally like ten times better.

I can wait a year sure, but I really don't want to. I can't stand it where I'm at anymore, I have nothing in common with most of the people and am an outsider to the culture.

>>7981383
you need the full course of calculus and ODE's before you can get into the bulk of engineering classes.

just bang out what you can and maybe think about double majoring.

>>7981364
put a proposal together and show it to your professor. nobody is going to let you just fuck around with their equipment without some kind of plan.

So you think I should go ahead with CS and work on all the technical courses related to engineering too? With a year of CS and all my basics done, that means it shouldn't be too tough to double major right?

CS doesn't seem too far away from engineering, I was hoping chemical engineering once I transfer internally

>>7981537
Meant for

>>7981526

>>7981537
>With a year of CS and all my basics done, that means it shouldn't be too tough to double major right?

pretty much

>CS doesn't seem too far away from engineering

depends. EE/CS is a very popular double major scheme because there is a good amount of overlap.

in general, CS and engineering are quite distinct, but the one advantage that you will have is that most undergrad engineering majors are total shit at coding or computer stuff in general because you don't really use it till like late junior/senior year. everything up until then for engineers is hand jamming with pencil and paper.

as a mechanical engineer, the one thing i wish i had more of a background in was computers.

>>7981560
This sounds good then
However it sounds like it would take quite a bit longer to graduate

I really hope to eventually aim for a masters in biomedical engineering, I'd imagine that CS would be very useful for many aspects of that

>>7981573
>However it sounds like it would take quite a bit longer to graduate

look, take it from someone who did the grind hardcore because "muh graduating in some arbitrary timeline". if i could go back and do it over i would have slowed the fuck down, took a lighter courseload, and probably worked some ez-pz shitjob on the side.

when you are lying on your deathbed, you won't regret that extra year or so you didn't work in industry, you will regret that you spent a good chunk of your twenties being miserable when you didn't have to be.

>>7981588
Hmmmm

This helps a lot, thank you

>>7980764
A slight skew? A longer whisker toward the higher values shows positive skew and vice versa.

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I graduated with a meme business degree and a low gpa a few years ago, but in my spare time I've (confidently) made it through spivak, rudin and some stats and mathematical methods texts. In a couple more years or so I'll have an equivalent of a math undrgrad. Is there an exam or something in the US I can pass and put on my resume to start shooting for better jobs? Similar to the way a GED is the equivalent of a HS diploma?

I just don't have the time/money to attend classes. I know my shit though.

>>7981679
Sure you do :^)

>>7980972
If anything it would be left skewed. It's a bit counter intuitive when you first learn about skewedness, but the reason we say it's "left skewed" is because the more extreme values on the left pull the mean towards them, and can skew the measure of center.

>>7981679
idk about any test you can take for certification, but you should just tell the employer what you can do in the interview.

>>7981701
That isn't counter-intuitive at all...

>>7981705
I'm worried I won't get an interview if I just put "rad math skills" or "read and understood rudin" on it. What if they've never heard of rudin? I need a 'bullet-point', if you will, that is recognized

>>7981718
No, there's no test you can pass and immediately get an equivalent to a 4 year degree. Barely anybody would go to college if you could do that.

What kind of job are you working right now? The best thing you can do for yourself is try to get some job in an analytical field right away, even if it's not 300k starting.

If you have experience, even a year or two, working with statistics in real life scenarios your qualifications won't mean much when you're applying for a job that needs stats; you can obviously do what they want because you've been doing it.

As for getting your foot in the door, I hate this piece of advice as much as the next guy but it's the best way; networking around will find you interviews a lot easier and will land you a position a lot easier too.

I have a probability question.

In a game there are 17 cards, 11 are red and 6 are blue. You draw three cards, how to you calculate the probability of the draw while also accounting for discarded cards?

The game is secret Hitler, for anyone wondering.

>>7981762
The probability of what? You never specified.

For line integrals of a vector field, does Int(F dot dr) actually mean Int((F dot dr/dt) dt)? And if so, how can they cancel the dts in the notation when dr/dt is part of the dot product?

What would a square of size (1+i) look like?

>>7981762
While J = 17 then

J(17/6 * [11^J] / J)

>>7980526
He just adds [math] \displaystyle 0=i\frac{x}{2}-i\frac{x}{2}=i\frac{y}{2}-i\frac{y}{2} [/math] inside each exponent and then combines them algebraicly. Not sure what it's useful for though.

>>7981808
Probably a square.

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Please help with with 33, 35 and 36. I'm really stumped and even a hint will do though I'd really appreciate a full solution to either problem.

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>>7981746
Thanks for the advice senpai. I'm not in a bad position but I can't help torturing myself over what could have been. Seems like I'm locked into underling-class now.

>networking around
Actually i'm pretty good at this. I picked business to study so I could spend my other time learning how to be socially competent. I was mostly successful.

>>7981824
probably proving the sum of angles in trig

>>7981794
Oh, sorry. The probability of the three cards being drawn. While accounting for cards already drawn, as it doesn't get reshuffled until necessary. Thanks

>>7981818
Sorry I didn't specify.

Three cards are drawn. So what I'm looking for is the probability of each draw (AAA, aab, abb, BBB) while considering the 11-6 split and discarded cards.

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>>7980526
I took calc three years ago and we learned about partial derivatives. However in calc one they teach you something called implicit differentiation or something.

Aren't they the same thing? Will there ever come a time when you don't use partial? So why do they even bother teaching this over partial?

>>7981718
>>7981906

third party software companies offer certifications for shit. most of them are test based. try microsoft, i hear people use their software.

look at CAD/CAM software, CFD/FEA software, planning/estimating/billing software. all the companies that make this shit offer certifications you can get that are mostly test based.

but lol if you think you can just cram 2 weeks and pass.

When balancing redox equations, does the charge of an ion change when you add a coefficient?

I.E. I have Br2 which becomes Br-. So, I make Br- into 2Br-.

Does the charge of Br- become -2 when it becomes 2Br-?

>>7981906
Usually you can get a job doing anything if you know the right people and have the skills for the job. After a certain amount of time working in the industry doing something that you don't have a degree but have experience is a huge plus.

I knew a guy who never got past his associates but worked in a lab with me and was one of the best chemists I've ever met. He originally applied for the job on craigslist and got it and then just ran with it.

Though at some point, like if you really want to move up the ladder at the company, not having credentials would really hurt you. That's why the same guy is still working in the lab and I'm the lab manager now.

Is there anyway to take a function f(x,y), and displace its values according to a vector field r(x,y)? For example if f(x,y) is 3 at the origin, and r is <1,2> at the origin, then 3 is added to the output at (1, 2). Is there a way to express this? Is there an algorithm to do something like this?

Balancing redox reactions.

One half reaction is I2 > IO3 (-)

So, I get I2 6H2O > 2IO3 + 12H+ + 10e which does not seem right.

Am I truly right or am I just fucking up?

Please help me understand this.

Why does 2sqrt(x^3) = 2x sqrt(x)

Explain to me the factoring process

>>7982184
Never mind I just realized that 2sqrt(x^3) is like saying 2sqrt(x)sqrt(x)sqrt(x) which is 2sqrt(x^2)sqrt(x) which is just 2xsqrt(x)

>>7982193
In case you didn't know, sqrt is the same as raising to the exponent 1/2 (and in general the nth root is given by exponent 1/n) and this makes the algebra much easier when you're given more complicated expressions

so 2sqrt(x^3)=2(x^3)^(1/2)=2x^(3/2)=2x^(1+1/2)=2x*x^(1/2)=2xsqrt(x)

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>>7982182

whole problem

I balanced the reduction part involving the chlorine, but the oxidation side with iodine is the issue.

I need to show that a set is a subspace of M22.
Are they asking me to show that the set is a subset of M22 and then that it is a subspace? or just subspace?

>>7982320
every subspace is a subset
not every subset is a subspace
only the ones that have their own vector space structure with the ambient space

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Stupid engineering student here, this is one of my homework problems and I'm frankly at a loss as to how to start it, any pointers?

>>7980526
(1) he just wants to change his variables from x and y to x+y and x-y, it's a well-known technique
(2) ignore his illiterate "And therefore", very few Math people know how to write Engilish

>>7981679

Do a distance learning degree, if you know the shit itll be as simple as turning up for exams. Im not american but i dont see why you wouldnt have it there.

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I left my brain at work, so I don't know what I'm doing anymore.
I'm trying to change the balance point of an object by adding weight to the end of it.
But I'm having trouble figuring this out.
See pic related.

Is there a massive list of equations to practise rearranging? I can only seem to find small amounts of questions that cover the basics.

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How do you do a mesh current to the pic related. This fucking thing is mocking me. It should be simple but I keep coming up with the wrong answer.

>>7982031
partial derivative and implicit differentiation are two completely different things

>>7982447
If they're both at the same length away on the fulcrum, L, then the torque is L(B-A) and the force applied at that point, L away from the fulcrum point is (B-A)

>>7982031
Partial is used when you have more than one variable for the function.

>>7982399
When a matrix M is orthogonal it has the properties:
MM^T=I
M^-1=M^T

The first property is the one you should use to show it. The second you can use to help you on your way.

>>7981679

just do a graduate certificate

Kind of a meta so I don't know exactly where to ask

how anonymous is 4chan now? Can it keep its users anonym in the future? Is it a good idea to do so?

also how many lawsuits where exclusively made against 4chan and it's owners and how can the lawyer handle this enourmous amounts (if there are) ?

>>7982552
This is pretty much saying you're going to post some fucked up shit to /b/ in a minute

Netsec by day here. 4chan is only anonymous to the users who you are talking to on a post. It does not anonymize anything else for example IP logs, which can be used to know everything about you.

>>7982516
Thanks !

>>7982560
nah I was wondering because I think in my country and many others 4chan couldn't exist legally. I'm not sure if thats good or bad tho.

>>7982578
Not sure. The government would probably let it exist but also happily extract data from it. In any case, worrying about anonymity is TORs domain, not *chan.

>>7981070

BUMP FAGGOTS

Please : )

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Sorry for highschool tier maths, but i suck at this shit.

Is this mark scheme wrong? I dont see how this makes sense.

>>7983062
Yeah, that don't really make sense. The distribution of the broken plates is binomial.

>>7982182
>>7982208
I2 6H2O > 2IO3 + 12H+ + 10e
+
clo3- +6e- +6h+ -> cl- +3h2o

now first x3 and second x5 etc etc..- you can continue on your own

when I was 17 i attended a year of college , didn't really take it seriously and failed half, maybe more of my classes.

i'm 21 now, and am completing my first year back at a different school now

this semester it looks like i'll be getting straight As in 4 classes and a lab, so at this school my gpa is a 3.8

my question is, will the university i'm applying to (a really good one) care about this? or will they look at everything and disqualify me for my dismal grades back then?

the average gpa at this uni is like 3.6-3.7, if my 17 year old year counts, my total gpa is like less than 3

I partially explained in my essay, but i don't know,

am i fucked?

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Can anyone explain to me in idiot terms how to interpret this ANOVA output table? I'm essentially trying to prove that the data found during the AT trials is more than the data from the A trials.

>>7980751
>>7980753
>[\math]
Try [/math] instead senpai

>>7982552
Try /qa/ next time.

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Anyone ever hear of something called Snap Circuits? I have their musical recorder kit and I'm trying to assemble it using as few parts as possible. Any advice?

http://www.elenco.com/admin_data/pdffiles/SCP01.pdf

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Can you faggots confirm whether this box plot is still considered left skewed despite both portions of the box (from q1 to q2 and from q2 to q3) being the same length.

T-t-thanks.

>>7982031
Implicit differentiation is simply taking the derivative with respect to a certain variable on both sides of the equation.

The "implicit" part of it is that you're assuming everything is a function of the variable you're differentiating with respect to.

Take a function f(x,y,z). What notation do I use if I want to differentiate it with respect to x and y only?

>>7983519
You can't differentiate wrt two variables at the same time. A derivative is directional, so you have to choose a direction.

You need to take the partial derivative wrt x, then the partial wrt y.

>>7983519
Just fix some number z, define the function [math]g(x,y) := f(x,y,z)[/math], and take the derivative of g.

I get the applications of basic indefinite integration, but I don't really understand the application of multiple integrals. What's the purpose of it? What is it used for?

>>7983552
Just as an integral of a single variable function can get you the area between curves, the double integral of a two-variable function gets you the volume between surfaces.

The integral of a density function equals total quantity, so you can find the mass of a two-dimensional plate if given its mass density function. You can then use other double integrals to find its center of mass.

Similarly, If you think of the total set of outcomes of an event as a plate with mass 1 and each particular outcome as a portion of the plate having a certain mass < 1, then you can find the probability of an event if given the probability density function. The cool part is that since it's a double integral, you can have 2 variables that determine each event. (For instance, find the probability that I will get an A in Math and and B in Chemistry).

You can also find area with a double integral if you set the density = 1.

>>7983698
Actually, the letter grades in the example I used wouldn't work. It needs to be a continuous value. So for instance, my wait time at the restaurant can be between 0 and 60 minutes, the volume of the table I'm seated at can be between 0 and 200 cubic inches. Find the probability that my wait time will be 12 minutes and my table will be 110 cubic inches.

Is the Law of Conservation of Energy the one that explains that if you throw an object up in the air at a certain velocity it will comeback down at the same velocity? Or am I thinking of a different law.

I have trouble understanding a basic principle behind electricity

I can imagine that voltage is the difference of the electrical potential between two points.

But what determines if electricity flows between two points or not.

If the voltage is high enough then there'll also flow a current if the two points aren't directly connected.

>>7983830
Electricity is flow of charged particles. The voltage shows how the particles will flow between points.
What are you confused about?

>>7983866
Take two points that are 2m apart in a room with air. Suppose the voltage between them is 100V. There'd probably be no current between them, right?

What if you increase it to 40kV?

At some point (if the voltage is high enough) there'd be a current between them and I don't understand when that point is reached.

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>>7984030

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>>7984035
>>7984030
I got r^3 instead of r. Can anyone help me with this?

>>7984038
Just rearrange and sub it in, how can you fuck this up? Is anyone over 18 on this board? Like I'm not one of those dicks who laugh at people who are still learning the basics but /sci/ loves to act like they are all tenured geniuses so questions like this annoy me. Be consistent guys, is this a board for school kids or researchers?

>>7980526
>>7982399
>>7982503
>>7983062
>>7984030
>>7984035
>>7984038

>being a macfag
>using a craptop

>>7984083

I use an Android phone, moron

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>>7982447

Write out the moments equation and it'll show that if the distance from A and B to the fulcrum are the same, the force pushing from the scale is equal to their difference, so yes.

>>7983881
As you're increasing the voltage, the system is reaching a point where the charged particles would gain more energy by traveling the gap, than staying on either side. This will be the point where dielectric breakdown occurs - the particles have enough energy to ionise the atoms and then a current can pass through.

>>7981679
Pass the actuarial exams

need some advice lads.

The current CC I attend requires 3 semesters of physics to be eligible to transfer to a UC. Im taking the first one right now, but i wouldn't be able to apply to any universities this fall because I would be taking the second installment in the series in the fall so I would have to wait another year to finish the required courses. The thing is, at a different CC I can apply for transfer after taking 2 physics semesters and they offer 1 physics course this summer and the second one in the fall.

My major is ME and I'm already 23 turning 24 in a couple of weeks. I didn't take school very seriously when I got out of high school and havent done shit since then other than go to school. I feel desperate to get a job and to transfer out already. Should I drop the current physics class, re-take it in the summer at a different CC and take the second part in the fall to apply for a transfer this fall for next fall admission??

>>7980883
Junior year in college I had a vector calculus class called calculus of several variables (not to be confused with multivariate calculus) and we dealt with path and surface integrals (as well as Green's theorem and Stoke's theorem) but I really haven't seen them since. I'm guessing you see them more in grad school?

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What's the most legit way to lighten skin? Are glutathione pills effective? I'm a 20 on the chart and am looking to get a few shades lighter

>be CS major
>good at high level math
>understand Graph Theory pretty well and other initially esoteric CS subjects
>awful at programming such data structures
>getting increasingly decent and more skilled at working with machine code and building assemblers in C
Am I going to be fucked if I try to enter a CS doctorate's program without being able to program theoretical data structures well? I've heard that analysis == grad school whereas compiler-building == industry

I also think a large part of the issue might be because I'm trying to do it in Java, but that can't be helped much. It's just starting to worry me because I make near perfect scores on the written exams but make B/Cs on the programming labs

>>7980526
Can anyone think of a home kitchen capable test for formaldehyde?
My fiancee is paranoid (with good reason) about formaldehyde in our vegetables. Some green groceries dip the base of stuff like cabbage in formaldehyde to keep it looking fresh on their shelves.

>>7984774
>with good reason
We're in China, shit like that happens all the time.

>>7981869
34)How did you define the operatornorm in the first place? Because what you are asked to prove is the definition most functional analysis books have.
35) probably cauchy schwarz
36) definitely cauchy schwarz

>>7983420
REEEEEEEEEEEEEEEE

Can you faggots falsify this. Looked all over the internet and in my textbook, cannot find anything.

>>7985401

Falsify. Kek. I mean clarify.

>>7984075
Did you do the fucking math? I said I did and got r^3. Show your math that gets a different result shitbag.

>>7984075
You can clearly see 1/r^2 = r>>7985463

Am I retarded or is there a typo in this question?

The volume of a cylinder is decreasing by 4 cubic feet per hour. When the thickness of the cylinder is 0.001 feet, the diameter is 500. If the height is decreasing by 0.0005 feet per hour, what is the rate the cylinder face is changing?

I get that the face is supposed to be changing size, but I'm reading this as the height and therefore the volume of the cylinder reaching 0 after two hours which would be much faster than the 4 cubic feet per hour would allow.

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can anyone give me some hint as to how I should solve this problem? I feel like I should use this Langmuir isotherm thing that the lecture notes talk about, but I am not entirely sure how.

due in 1 hour pls help

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Bonjour sci,
I and correction finding different results for this.
I dont know what I did weong and I am hoping for your help.

This is a semi infite solonoide. I have to find the magnetic field in a point of his axe created by an element of length dz.

>>7981797
You are correct. The reason they might do some handwavey shit and say they are cancelling out the dt is because dr/dt*dt actually is just equal to dr.
It's not an actual algebraic cancellation but it sure as hell looks like one and your concern is warranted.

>>7984449
Thanks, that's exactly what I wanted to know.

yo Deutschfag here, I am considering going to the US for a phd in physics. I heard phds in the US usually include 2 years of normal coursework and studying. However I did already do a master's here.

Are there research only phd programs? Do you get paid for doing research and working as ta or do you rely on scholarships? What is the situation like in general, would you recommend a phd in the us?

Hey /sci/, I need some advice/want to hear some stories.

Going into 1st year mechanical engineering at Colorado School of Mines. Mechanical engineering is supposed to be easy according to this board, but I'm still nervous about doing well. Could some mechanical compatriots tell me about their experience in college, what to expect, and whether or not they would change majors if given the choice?

Inb4 solidworks

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Is this a decent precalc book. Will I be ready for calc after working thru this?

>>7980526
I'm uploading textbooks on /tg/, because they have a pdf upload
Does anyone have a good djvu to pdf converter? I'd be able to post a lot more if I had such a thing.
Here's the thread:
>>>/tg/46460931

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having a brainfart today

let f(x) = 3 / (x-2)

evaluate f(f(x))

>>7980526
/sci/ do you find it sad that no one will ever know everything that humanity knows? doesn't it feels that no intelligence will ever be truly "complete"?

What's a good equation editor software that will run on a mac and windows??
MyMathLab won't work

>>7986329
I'm also a freetard so something open source and libre (FLOSS) would be dank, FSF sorta shit ya dig?

>>7981383
>am an outsider to the culture
You're on 4chan, get used to being an outsider.

Can't you just go in as undeclared, start taking all of your prereqs, and then formally declare your major when you're allowed to? Is this a school in the US?

>>7981560
>most undergrad engineering majors are total shit at coding or computer stuff in general
This so much, it's absolutely baffling.

>>7983329
I bought one of those for my nephew lol.

>>7984713
There's a lot of compiler research going on right now, just lookup Alex Aiken from Stanford and go from there. But yeah, program analysis is a very big part of it.

>>7986240
fucking moron

I'm stuck doing this stupid easy line integral:

Let C be the regular curve from (1,1,1) to (1,3,4). Find [math]\int_C 2xyz\:\mathrm{d}x+x^2z\:\mathrm{d}y+x^2y\:\mathrm{d}z[/math].

Now I know that by inspection you can see that the integrand is path independent and you can find it through the gradient of the function yzx^2, but I tried doing it as a normal line integral and keep getting the wrong answer. It's 7 btw.

>>7986240
f(f(x))= 3 / [( 3 / (x-2) )-2]

>>7986578
Nevermind, I'm retarded, forgot to parametrise correctly

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I took a shot of methanol vapor straight to the dome a couple hours ago. How long do I have before I go blind?

Stuck on this problem
--
Let [math]A[/math] be a [math]7 x 7[/math] matrix of rank [math]5[/math]. We know that [math]3[/math] and [math]4[/math] are eigenvalues of [math]A[/math]. Is [math]A[/math] diagonalizable?
--
I think the way to approach this is to show that [math]A[/math] has less than 7 linearly independent eigenvectors, I'm just not sure how to do that. Any ideas?

Any general strategies to reading academic papers? I can get through the overview sections and get a good basis on what is going on, but once it gets into the really detailed level stuff it all just goes over my head.

>>7986902
ethanol (normal alcohol) is the cure for methanol poisoning, but it is too late now

>>7986926
No, it's not diagonalizable. Jot down the information you know. Dim(A) = 7 (7x7 matrix) and rank(A) = 5. By rank/nullity theorem dim(A) = rank(A) + nullity(A), 7 = 5 + nullity(A), so nullity(A) = 2.

So now, think. By definition the dimension of the eigenspace (denoted E) is the same as the sum of the geometric multiplicities of the eigenvalues. So, in order for A to be diagonalizable, dim(E) = 7 (you get a 7x7 matrix, S such that S^(-1)AS = D, some diagonal matrix similar to A). Basically, you need to be able to come up with 7 linearly independent eigenvectors to span the eienspace. Note, the geometric multiplicity (m) is equivalent to the dimension of the nullspace of A-I (I is the identity matrix) = rank(A). Because 5<7, there aren't 7 linearly independent eigenvectors to build the S matrix to diagonalize A, so A is not diagonalizable.

>>7987024
you are forgetting that 0 can be an eigenvalue, so rank(A) is not an upper bound for the number of possible eigenvectors.

>>7980534
dumb lazy nigger this is a SQT you nig.

>>7987035
Rank(A) is still the upper bound for the sum of geometric multiplicities. I think this would be different if every eigenvalue was 0 (I'm actually really not sure, linear algebra is my Achille's heel in math), but the question says 3 and 4 are eigenvalues, so this isn't the case.

>>7987054
again, that is only highballing the sum of geometric multiplicities of linearly independent eigenvectors corresponding to non 0 eigenvalues. The eigenvectors corresponding to 0 eigenvalues are not approximated at all by the rank. By that logic, the 3x3 matrix with a single entry 1 in the upper left hand spot (0 everywhere else) has, at most, one linearly independent eigenvector, but it has 3 (eigenvector [1,0,0] corresponds to eigenvalue 1, eigenvector [0,1,0] corresponds to eigenvalue 0, and eigenvector [0,0,1] corresponds to eigenvalue 0).

>>7982512
If I'm understand correctly:
Partial would be something like f(x,y) = x^2*y^2 and I'd find partial x and partial y

Where as implicit would be f(x) = x^2 and I'd just take the derivative d/dx?

I suppose it would help more if I gave an example. Like they wanted us to take the derivative of the equation of a circle, or something like :

f(x) = x^2 + y^2 and then compute the derivative with respect to x.

I remember having to do a fuck load of work when I would get the same answer just taking the partial derivative. I'm just curious why they had me go through all that aggravation if you could just solve it in one step as opposed to a million

>>7987066
Then how would you go about proving it? Eigendecomp maybe? I don't know much about that.

I have a data file with lots of lines. Each line is an update to a variable.

I want to be able to see which variables are typically updated within the same 10 line periods.

Can someone point me to what I need here?

>>7987142
An update to a different variable*

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>>7986115
I'm not familiar with that book to be honest, when I self taught it in high school I used pic related. What are each of the chapters? Does it cover rational functions, limits, and trig (unit circle all the way up to the trig identities)?

>>7986240
f(f(x)) = 3/((3/(x-2))-2) = 3/(((7-2x)/(x-2))-2) = 3/((11-4x)/(x-2)) = (3x-6)/(11-4x). Unless I fucked up the algebra somewhere, that's it.

>>7986926
[math]
\begin{pmatrix}
1 & & & & & & \\
&2 & & & & & \\
& &3 & & & & \\
& & &4 & & & \\
& & & &5 & & \\
& & & & &0 &1 \\
& & & & & &0
\end{pmatrix}
[/math]
is not diagonalizable, has rank 5 and 3/4 as eigenvalues.
Remove the one in the jordan block for 0 and you get a diagonalizable matrix with the same attributes.
Thus you just can not know, if a matrix is diagonalizable without more information like A symmetric/normal

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I'm working on the 2nd chapter of Terry Tao's Analysis 1 book. Please help me review the proofs I have done on a problem, I have never done analysis before and the book does not have its solutions available. Here is the exercise:

Prove that if a is a positive number. Then there exists exactly one natural number b such that b++ =a.
(Here, b++ is applying the increment operation on b, i.e. b++ = b+1).

Here is my proof using contrapositive:
Let d++ = a = b++ and d =/= b.
But by axiom number 4 in list of Peano's axioms (pic related), it is a contradiction since d++ = b++ implies d = b.
There fore d must be equal to b.

The book also recommends using induction to solve this, so here is my attempt:
The base case: 1 is a positive number, it only has a unique predecessor that is 0. (I don't really know if I need to prove this, If I have to, then I don't know how to prove it at all).
Let a be a positive number with a unique predecessor b so that b++ = a. By Peano axiom #4, a is also unique.
Now, a++ = (b++)++. But b++ = a and a is unique. Therefore a++ only has one unique predecessor. This conclude the induction.

>>7986646
>>7986646
I feel like that's usually where the problems with line and surface integrals happens.

Is first order mathematical logic hard or am I just dumb?

>>7987362
Please someone help me on this.

>>7987362
I don't know what Tao is up to, PA has various lists of axiom that are equivalent in some way. I looked up PA in my recursion theory book I have right in front of me, and axiom 1 is that sucessor function is injective, so done.

Another way to think about this is induction I guess, but just using the syntax of PA.

Let 0 be a distinguished constant, and S as the successor function in L(PA). Then S(0)=S(0) by the mere fact that the sequence of symbols is the same. Assume S...S(0)=S...S(0) be the successor function applied to zero n times. Apply S to each side again, then the sequence of symbols is the same. Remember the equality symbol I am using here is in the metatheory.

So from a formal syntactic system, this is obvious.

>>7980526
I'm going to be a father in 5 months, how do I educate my child so that he doesn't grow up fucking retarded? Home-school? All of my colleagues' sons want to be artists or lawyers or whatever the fuck. I don't want that.
I'm and engineer and my wife is a Physicist by the way.

>>7987496
Don't worry, your child will be similar to you in intelligence and interests just through genetics. All you really have to do is feed them, protect them, and be yourself around them.

>>7980526
I'm trying to create a "multipurpose calculator". I know C,C++ and Python.
How do I make a program that creates a window with which the user can interact?

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Need help finding the area between these two functions on #9.
Finding the bounds by setting them equal to each other is first right? What's next?

is Brown/Churchill good for fourier series? i have an intro proofs w/ discrete math course and the calc sequence up to odes under my belt

>>7989387
Loom up GUIs.
I was gonna make something like that in Python

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What's the best way to release the same chemicals in the brain as are released after masturbation?

Or is this thread just for math?

>>7989960
>What's the best way to release the same chemicals in the brain as are released after masturbation?
I'd suggest masturbating

>>7989965
But I'm trying to stop ;-;

>>7989977
why? are you a fag or something?

>>7989977
...why?

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>>7989999
>>7990000
For The Lord.

Also, because its a gross habit and I don't feel I could become the best man that I can be if I'm noodling my noodle everynight.

pls don't bully

>>7989957
What do you mean?

>>7990026
I'm not him but something like Tkinter for python would let you make buttons and stuff like that

alternatively you could make a web calculator with html&css and javascript and make it really pretty, it would probably take a day to learn enough of html and javascript to do that

>>7989910
Integrate those fuckers over their overlap interval and compute the difference

>>7989387
Gtk is a GUI library for C/C++. Bit of a learning curve but not too bad

In probability theory, is there an easy way to visualize the relationship between the pdf of [math]X[/math] and the pdf of a function [math]U(X)[/math]? Say [math]X \sim N(0,1)[/math] and [math]U(X)=e^X[/math], is there any way to predict what the resulting pdf will look like without calculating?

If a man dies instantly whilst having a boner, how long will this boner last? Can it be forensically confirmed that the man did indeed have a boner at the moment of death?

>>7990329
Priapism is common after death.

What reasoning lies behind the average expiration time of 70 years on copyrights in most countries?

Considering the pace of developement nowadays it seems like it could cause quite some harm.

>>7985404

I can clarify that your brain is skewed pretty far along the spectrum retard

what makes a carbon-fluoride bond so strong and why is it stronger than a hydrogen-fluoride bond?

can you get tetanus from a pinprick?

Can someone explain to me euclidean planes and R^N?
I can't wrap my head around finding the limits of a series like A = [0,1]\Q

Can you make dry ice from other gases?

>>7990990
Isn't dry ice by definition solid carbon dioxide?

Why do all my number theory books have to have logical connectives, for fucks sake I hate them I always make a mistake when reading those.

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The pic shows 5 types of question about putting things into other things, for 3 objects and 3 boxes its easy to brute force and get
>a) 27
>b) 6
>c) 10
>d) 5
>e) 3

But im interested in doing it for r objects and n boxes, the first 3 are trivial
>a) r^n
>b) r! (assuming r = n)
>c) C(n + r - 1,r)

But I cant think of a general way to do d and e, google says to use generating functions or recursion relations, but im not sure how to apply them to this.

>>7980526
where do I fuck up?
[eqn]
\log_2 (x+12) * \log_x 2 = 1 \\
\log_x 2^ {\log_2 (x+12)} = 1 \\
\log_x (x+12) = 1 \\
x+12 = x \\
12 = 0
[/eqn]

>>7991006
Can you make solid frozen blocks of other gases as easily as dry ice?

>>7991229
> Can you make a solid that sublimates at standard pressure?
Idk. Start checking those phase diagrams.

>>7991243
Okay, that was pretty useful. Carbon dioxide stays solid at a much higher temperature than other common gases in the atmosphere. The noble gases basically don't solidify. I had a lot of trouble finding a diagram for O2. I just kept getting results for water.

>>7991182
It probably means that the original statement cannot be true.

>>7991182
Try plotting it.

I bought a 99% cacao chocolate bar and a 90% cacao chocolate bar today and I just noticed that the 90% one feels a lot heavier than the 99% one altough they have the exact same size
and then I saw that the 99% one is only 50g and the 90% is 100g

so higher cacao % = chocolate is lighter?

why?

>>7990651
The fuck do you mean ?

>>7991531
correlation does not imply causation

what to expect out of intro mechanical engineering course? can I practice it somehow before taking the class?

>>7989999
>>7990000
wasted quads

>>7991613
Do you have to use induction? You can do that algebraically without too much trouble. The induction way should be pretty simple as well, just follow the steps - where are you getting stuck?

How do I prove
\sum_{n=0}^{k}\binom{k}{n}=k^2
using induction?
I had a short course on mathematics and we were discussing power sets: the power set of a set A with k elements has k^2 elements.

>>7991622
Fuck me, I deleted it because I made a mistake in the calculations and then I forgot the math command: >>7991623
I did an intro course on math and the topic was power sets: if a set A has k elements, its power set would have k^2 elements. The professor appealed to common sense for the answer but it didn't satisfy me. I deduced that this equation needed to be proven using full induction. I asked the prof and he said it's doable but we never got to what was to be proven.

>>7991622
Continuing: the initial step is easy. It's the induction step that I get stuck at. It's been a while since I did this so it's not fully clear to me anymore, but you can expand the sum. Next you have a term [math]\binom{k+1}{n}[/math]. If you eliminate the 1 you end up with a factor that you can't get rid of. I believe I also tried "folding" the series since [math]\binom{k}{n}=\binom{k}{k-n}[/math].

>>7991654
Do you realize you have a typo? It's [math]2^k[/math], not [math]k^2.[/math]

>>7991631
>Fuck me
ok

>>7991673
I realize that, just as I realize I can't type on a saturday night, apparently. It's obviously 2^k elements.
I should re-try to solve the problem since it's been a while, but if you understand the problem I'm facing you can try to solve it too if you like.

>>7991654
Use the fact that [math]\binom kn + \binom k{n+1}= \binom{k+1}{n+1}[/math]

>>7991746
Thank you for the hint but I don't quite get it yet. This is how I see the problem: knowing that summation to [math]k+1[/math] yields [math]2^{k+1}=2 \cdot 2^k[/math] which is twice the original series. This implies that I need to turn all [math]k+1[/math] into [math]k[/math], then somehow end up with the original series times two. However, the derivation for every term yields a unique coefficient.

I'm probably just making a stupid mistake but I really don't see how to solve it.

>>7982320

They are asking you to prove subspace. Test that the set is closed under addition and multiplication in M22

Would it be worthwhile rewriting my BAI EE thesis in Latex? I don't really like it, I think it makes documents seem anemic and super-dull, but I'm not the one marking it.

>>7986329
>>7986341
BUMP

On a graph of trig functions, is pi considered one wavelength my boys?

>>7992629
yeah

>>7992696
ty.

can you explain to my retard brain how to determine x intercepts of y=cos(x)?

I get that it's pi/2, 3pi/2, 5pi/2 in both directions, but how do I write that concisely?

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Physics major messing around with some maths here.
Using the substitution [math]u=\ln x[/math] I arrived at [math]\sum\limits_{n=0}^\infty n!e^{e-n-1}[\frac{e^{te}}{(t+1)^{n+1}-1}][/math].
How do I continue?

I'm trying to show that a set is a subspace. I've proven that it contains the zero matrix and I've shown that the sum of two elements in that set can be zero and scalar of an element can be zero. Is that all i have to do?

I have a jar with 20-30ml of hcl from about 10 years ago when i dissolved a penny or some copper in there because I thought it was cool or some shit. The liquid in the jar is now blue, which was what i was aiming for.

However i've recently read that hcl doesn't dissolve copper unless it's in the presence of oxygen so I'm assuming it just used the oxygen dissolved in the dilute hcl because the jar is sealed.

My stupid question is why it smells so much worse than normal hcl and why it slowly turns from green to blue after all the copper is dissolved.

Am i right in assuming that it's just going from Copper 1 chloride to copper 2 chloride and if so why does it do this.

[math]\sum_{n=0}^{4} sin \frac{\Pi n}{2}[/math]

ok, so why couldn't I just simply pull out sin pi/2 and then multiply that by the summation? because the answer to this summation problem is 0. It doesn't make any sense to me .

>>7992910
[eqn] \int_{x \in [0,1]} \frac{x^t - 1}{\ln(x)} dx = \int_{x \in [0,1]} \int_{s \in [0,t]} x^s ds dx [/eqn]
[eqn] = \int_{s \in [0,t]} \int_{x \in [0,1]} x^s dx ds [/eqn]
[eqn] = \int_{s \in [0,t]} \frac{1}{s+1} ds [/eqn]
[eqn] = \ln(t+1) [/eqn]

>>7993205
sin(pi/2 *n) isn't sin(pi/2)*n
it's notation to add sin(0) + sin (pi/2) + sin(pi) + sin(3pi/2) + sin(2pi).

>>7992834
You could write that as ((2n-1)*pi)/2 for any integer, n. You get the x-intercepts of cosx by finding where cosx = 0. If you think back to the unit circle, because cosx is the same as the x value for any angle, theta. So, cos(0) = 1 because 0 radians is the point (1,0). Likewise cos(pi/2) = sqrt(2)/2 because the unit circle is (sqrt(2)/2, sqrt(2)/2) for that angle. You find that cos(pi/2) = 0 because it's the point (0,1). Because cosx has a period of 2*pi, you know that cos(pi/2 + 2*pi) = cos (5*pi/2) = cos(pi/2) = 0. This can be generalized as x = 2*n*pi + pi/2 for any integer, n. The other point on the unit circle where the x coordinate is 0 is cos(3*pi/2) or cos(-pi/2). Again, because the period is 2*pi, cos(3*pi/2) = cos(2*pi + 3*pi/2) = cos(7*pi/2) = 0. This can be generalized as x = 3*pi/2 + 2*n*pi for any integer, n. Therefore, the x intercepts can be generalized as x = pi/2 + n*pi for any integer, n. Or you can write it as x = (2*n + 1)*pi/2. I prefer the second example because 2n + 1 is the generalization for any odd number, but the first example illustrates the period of cosx.

>>7993295
>>7992834
> Likewise cos(pi/2) = sqrt(2)/2 because the unit circle is (sqrt(2)/2, sqrt(2)/2) for that angle.

My bad, that's supposed to be cos(pi/4) not cos(pi/2)

>>7993292
yeah but... couldn't I have have written sin(pi*n/2) as sin(pi) * 1/2 * n, which I then could have written as sin(pi/2) * n ??

>>7993308
No, you can't pull the n or 1/2 out of sin. You could if it was just multiplication, but sin(pi*n/2) =/= n/2*sin(pi). In this example specifically, sin(n*pi/2) = n*sin(pi/2), but that's just because sin(pi/2) = 0. There are some trig identities that allow you to play around with what's inside the sin function (like sin(2x) = 2sin(x)cos(x)), but you can't distribute like you would with multiplication.

>This study includes a mathematical description of the fields, an examination of the basic laws governing the generation of fields, and a study of interactions with dielectric and magnetic materials. Maxwell's field equations are introduced. Applications of electromagnetic fields such as radio, televisions, transformers, electrical motors and generators are examined, as are electrostatic painting, magnetohydrodynamics and beam control in a synchrotron. Naturally generated fields such as the earth's magnetic field and the electric fields causing lightning are also discussed
This is the unit description for second year EE electromagnetism and I'm wondering if there would be any recommended books I could self study with in preparation as i've heard it's relatively difficult and I'm pretty bad at the topic.

>>7981869
33. I dunno, that was my definition of the operator norm so I would need to see how your book defined it

35 a. Set x=y
b. By Cauchy-Schwarz, you have for all x of norm 1, [math]|\langle x,y \rangle| \le ||y||[/math], therefore [math]\sup\{|\langle x,y \rangle|, ||x||= 1} \le ||y||[/math]
Conversely, setting [math]k = \sup\{|\langle x,y \rangle|, ||x||= 1}[/math], we have for each [math]x \ne 0[/math], [math]|\langle x,y \rangle | = ||x|| |\langle \frac{x}{||x||}, y \rangle | \le k ||x||[/math]. Since the inequality is true for x=0, we have [math]|\langle x,y \rangle | \le k||x||[/math] for each x and therefore [math]||y|| \le k[/math] because of question a, which concludes.

36. is more or less the same as 35 a., I'll let you figure out how it works (hint: use question 33)

>>7984030
>>7984035
>>7984038
Anyone?

Is there any website where i can exercise my shitty factorization skills?

>>7989960
do drugs or find someone to cuddle with

>>7991631
>>7991623
you probably mean 2^k.
proof is basically taking the binomial theorem for (x+y)^k and plug in x=y=1

I don't understand electricity and magnetism, despite getting an A in the course. What are some resources for me to study and gain an intuitive understanding of it?

Also, fucking magnets how do they work.
Specifically, I understand power is generated by rotating a permanent magnet, but where does the electricity come from? The electrons aren't just generated, so they must flow from somewhere I guess.

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In the general definition of the Néron-Tate height [math] \hat{h}_L(P) [/math] (https://en.wikipedia.org/wiki/N%C3%A9ron%E2%80%93Tate_height) of a point P on an abelian variety A we need some symmetric invertible sheaf L on A.

I learned the specific case from Silverman's book where A is an elliptic curve defined over a field K and [math] \hat{h}_f(P) [\math] was defined from some even function [math] f \in K(A) [/math]. How do I go from the invertible sheaf point of view to this specific case? I'm having trouble seeing this sheaf.

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If the force of gravity on pluto is only 0.62 m/s2 how can it hold on to it's moons?

Am I correct in stating that house prices are an example of discrete data since they can only take particular values which are defined by the monetary system? E.g - a house cannot cost 200, 000.3333333 as it's a value outside the boundaries set by the monotary system (we use 2 decimal places to denote pence/cent).

>>7993959
Technically correct, but something like this is mostly still modelled like a continuous function.
A better example for a discrete value would be number of houses, since it can only take natural numbers

>>7993978

The question I'm trying to answer is "are house prices an example of continuous or discrete data?".
Keep in mind this is high school level math and I've not even touched functions as subject in themselves (have only covered things like sin, cos, etc functions).

>>7993989
well your reasoning is absolutely correct and is the right answer to the question.

I'm just saying you could also argue otherwise and many people do that when they model costs.
At some point when you want to make a model for a particular system, you have to decide if you want to work with discrete or continuous models or something in involving both.
Continuous models are generally more easy to analyse, since you can tackle the problem with everything you learn in calc for example.
That's why things like costs are generally modelled as continuous .

>>7994004

Okay thanks mate. And the stuff you've mentioned sounds interesting. I'm looking forward to calculus.

I have a stupid question:

As a kid, I used to think that everything in the universe had "weak points", that is, that you could do basically anything if you were to "hit" a certain spot of a body with minimum force, put infinite precision (for example, breaking a boulder with an infinitesimally precise hit.)

Now, after all these years, I find this ridiculous, of course, but I'm still no expert at physics. My question is: this is impossible, right?

Where can I get some good paper books for writing down math problems?
I'm looking for some that has thick paper, a wired back and either blank or dotted sides instead of lined or squared.

>>7994080
[math]\frac{force}{area}[/math]
Assuming that the force = 1 and that area approaches 0 from above it would technically be indefinite.

>>7993370
sin (pi/2) =/= 0, it equals 1.

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how do you get to this exact result by multiplying logarithms without a calculator?

inb4 am i dumb?

>>7994592
for example, ln(8)=ln(2^3)=2ln(2)

>>7994600
god damn it.

thanks

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How does one solve this type of problems? I searched all over for ''graph theory'' but I couldn't find anything that helped me. I had to count one by one but that's retarded.

>>7980526
Forgive me if this is low-key, but I'm a calc 1 student so that's only natural for me.

Can l'hop's rule be applied to any limit? Is there any sort of situation where I shouldn't, at my level of math?

>>7994795
desu on this scale this just seems like a counting problem

if you wanted you could compute the sixth power of the adjacency matrix though and check the corresponding entry for those vertices

How difficult is it to self study philosophy and literature in a serious manner while pursuing a physics degree?

>>7994836
Depends on how serious. Actual philosophers probably wouldn't see philosophy or the "study" of literature as anything but a hobby. "Serious" philosophers become philosophy professors.

>>7980526
a = a + b - b

>>7994812
how about you read up on the theorem.
google is your friend

>>7993894
It's moons are revolving around the 'planet' at a much slower speed.

>>7994827
So, in the end I do have to count each of the paths.

>>7992960
The two things you have to check are:
1. It must be a vector space.
2. It must be a subset.

Show that the elements have an additive inverse, a zero element (additive identity), adding any two vectors gives you a vector in that vector space, and any vector multiplied by a scalar is in that vector space.
To show it is a subset, you must check to see that all elements of the set are part of the super set.

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>>7980526
Some mathematician, please save me from the nothing I've become.

Please tell me where and how I fucked up in pic related. And if possible tell me what would be the correct statement.

By the way, what I'm trying to negate is the definition of a limit.

I've only ever bothered learning Newtonian Physics
Is the new stuff any good?

>>7994894
why do you think what you did is wrong?

>>7994894
i can't read these monkey symbols, can used words?

>>7994913
ok i read your symbols and it's fine. if i'm reading it right it looks good.

>>7994909
Because in this subject I have so far 3 As and 1 C. Guess what was the kind of problem I fucked up that got me that C? I am a disgrace to family.

Now I have nothing else to do but assume I am a moron, until proven otherwise.

Are you telling me that what I did is correct? If so then amazing.

>>7994913
Eh, I usually don't know how to read it properly.
Anyways, last statement:

>There exists an epsilon larger than 0, and for all delta larger than 0, so that the absolute value of x minus x0 is smaller than delta and the absolute value of of f(x) minus the limit is larger than or equal to delta

>>7994916
Oh, okay then.

This is the hardest problem I was given in my practice set. What do you think is at this level so that I can try? When I google quantifiers problems I only see the most basic of shit in .pdfs, and then the stuff in math forums I cannot even begin to comprehend.

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This is probably really easy but I'm stupid and tired as hell.

One of these graphs belong to the function f(x), the other one to f'(x). Which is which, and why?

Find the smallest real number y for which the following is true for all real x : sin(x)+2cos(x)<=y I would be grateful for some help. Thanks

How do you guys deal with the headaches and fatigue resulted form study?
And with that awlful feel you get when you don't have a clue of a solution and you brain keep pushing your brain?

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>>7994916
Did another just to be sure. I have a midterm tomorrow and I want to ace it to the moon and back.

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Discrete math is killing me.

I understand the first part is false and second is true. How do I prove these?

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this is probably really easy but i genuinely have no idea how to solve it... The answer is 6 multiplied by the square root of 2 plus 12... What steps do you take to get that (I really appreciate the help)

>>7994954
i dont know if this is bait but ill answer it anyway. distribute the -3 to radical 2 and -4 and you get -3sqrt(2)+12+9sqrt(2) and you combine the radical to get 6sqrt(2)+12

>>7994517
you right, I missed that

>>7994930
Look at the gradients at x=0 and note that they're both positive.

>>7991577

How large is the major at your school? The more students in your class, the more bullshit they'll make it so that people switch to something else. If you aren't dumb or unmotivated, you should do fine.

>>7994942
Chill out for a bit, watch a movie or something. Just make sure your breaks aren't too frequent and you're being productive when you're off your break.

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Say I've got two different functions, F(x) and G(x). If I wanted to write down that they are not the same function, should I write "F(x) != G(x)" or "F != G"?

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Someone help me. I must calculate the electric force of those charges. The question says to calculate the forces in the directions i, j and k applied to the charge indicated by the arrow. The dimension of the dice is l = 1.5cm. Any solution that I could make?

>>7995147
F =/= G
To me F(x) =/= G(x)
Could be for all x, F(x) =/= G(x), or at the value x previously stated F(x) =/= G(x)

To be overly explicit you could say there is a x such that F(x) =/= G(x)

For a continous string of infinite length the wave equation solution can be written as int("travellingwave exponential"*A(k)dk), my question is how would you find the A(k) from initial conditions, my initial guess was that you could just do the fourier transform at t=0 and from there you get the A(k), but wouldn't the A(k) need to be a function of time? If a wave starts at x=0 and travels forward then wouldn't the A(k) at t=0 x=100 or something be 0 and then after some time passes become nonzero when the wave reaches it. the only equation for A(k) that ive seen in my lectures is related to f(x) not f(x,t). looking in my textbook i see that they use C(k,t), but then make no relation this to initial conditions. They do however show f(z)=f(x-vt)=int(A(k)*"travelling wave exponential"dz) but when i make the same substitution z=x-vt in the expression for A(k) it seems like you would have to already have an expression for f(x,t) (or f(x-vt) ) which seems like it would be pretty useless since you use the A(k) to solve for the f(x,t)
>>7994930
if the derivative is zero then there is no change in value of the function, so a zero on the derivative corresponds to a flat area.
>>7995166
define your i j k vectors as being along the edges, then you can use simple geometry to decompose the radial vectors along these components, then you know that the net force on the charge in each will be the superposition of the forces in that direction.

>>7995242
>>7995166
that should be the net force on the charge in each direction will be the sum of the forces in that direction

>>7995147
why couldn't you write that? you're probably working with a definition of function that defines them as sets anyway

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What species is this and what do I feed it aside from the lettuce it came in?

>>7995271
/an/ here
It's a recluse

>>7995248
>>7995242
doing a dot product help?

>>7995282
/an/ sounds like a shitty board.

>>7994080
I'm assuming you mean if you were to hit the boulder at the perfect spot, not if you had an infinitesimally thin object to poke it with? My interpretation is that if two objects have a potential energy between them, your [math]\int \mathbf{F} \cdot d\mathbf{x}[/math] would have to be larger than that potential energy to break them apart even if you were perfectly efficient.

>>7995299
thats pretty much what you are doing. if you define i along the top right edge ("closest" to the screen) and k down along the verticle edge where the charge is at then the radial vector from the charge to the charge +q at the bottom will be <1,0,1> then to take the force component in each direction you dot the radial vector with i j and k seperately and you multiply each result by q^2/r^3 to get that component. but what you are really doing is just multiplying the magnitude of the force q^2/r^2 by the cosine of the angle between the radial vector and the unit vector you are working with. with this cube those angles are really simple so you should just work with that instead of with dot products, just keep track of the signs with your intuition. all the angles will be either 0 or 45 degreees because it is a cube

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Hey anon how do you get the final answer from the previous line? See attached pic. Thanks. I such with trig functions.

>>7995361
The same way 2 apples + 2 apples = 4 apples

>>7995361
...it's 2(thing) + 2(thing) = 4(thing)

you have to multiply the secants together to get it in the same form, but

>>7995361
[math] 2 u uv + 2 v u^2 = 4 u^2 v[/math]

>>7995361
It's [math]2\tfrac{tan(x)}{cos^2(x)}[/math] on both, you're literally just adding them

Just to rephrase my question, for an infinite string with tension how would i write the solution as an integral over k of travelling waves? more specifically how would i find the coefficients A(k) given some initial conditions and do these coeficients change over time? if so how would i deal with this. dont need a direct answer just some sort of direction.

>>7994953
I'm not sure what max(D(n) ^ D(m)) means, but if it means max(D(n) ∩ D(m)), then it clearly does not necessarily equal GCD(n, m) since n = 2, m = 4 is a counterexample to the asserted equality.

The second equation is a famous identity of Euler's totient function (Euler's totient function is the function |D(n)| in your notation).

For each divisor d of n, define the set S(d) := {x ∈ {1,…, n} | gcd(n, x) = d}. Then the collection of all such S(d) forms a partition of {1,…, n}. This is because (1) any member x' of {1,…, n} belongs to one such S(d) since gcd(n, x') is always some divisor of n, and (2) any element x' of {1,…, n} cannot belong to both S(d) and S(d'), d ≠ d', for that would mean both gcd(n, x') = d and gcd(n, x') = d'.

Therefore [eqn]n = \sum_{d|n}|S(d)|[/eqn]Now since every y ∈ S(d) is of the form dy', with y' coprime to n, there is a correspondence between the elements of S(d) and the numbers y' smaller than or equal to n/d that are coprime to n. But the numbers y' smaller than or equal to n/d that are coprime to n are also coprime to n/d and thus constitute the set D(n/d). Therefore |S(d)| = |D(n/d)| and [eqn]n = \sum_{d|N}|S(d)| = \sum_{d|n}|D(n/d)| = \sum_{d|n}|D(n)|[/eqn]

>>7995601
Thanks a lot, the second part makes a lot more sense now.

The first one is supposed to be false and I somehow need to prove that it's wrong.

>>7994877
Yeah, but the 6th power of the adjacency matrix is the easiest way to do that and I'm sure was the intended way to solve the problem.

>>7994930
A is f'(x) while B is f(x)

I figure I should post here instead of making an entire thread. Recently took the GRE exam and fucked up on the reading comp and quantitative sections, but scored a perfect score of 5 on the essays for the writing section. I will be taking it again, but is it ok to just skip the writing section and just send two separate scores to schools so I don't have to bother doing it?

>>7991016
The generalisation you are looking for for e) is the partition function [math]p_{\le n}(r)[/math] which gives you the number of ways to partition r into n parts or less. The most 'natural' way to get these numbers is to consider the expression [eqn]\sum_{r = 0}^\infty p_{\le n}(r)x^r = \prod_{s=1}^n \frac{1}{1-x^s}[/eqn]which is also known as the generating function of [math]p_{\le n}(r)[/math]. How it works is that the right side is meant to be interpreted as the product [eqn](1+x+x^2+\cdots)(1+x^2+x^4+\cdots)\cdots(1+x^s + x^{2s}+\cdots)\cdots(1+x^n + x^{2n} + \cdots)[/eqn]The result of expanding this monstrosity is a bunch of terms of various powers. Some terms may be produced more than once, in which case that means that there are multiple ways to multiply one term from each factor, and hence multiple ways to add the exponents of the n selected terms, to arrive at said term. The coefficient [math]p_{\le n}(r)[/math] of the term in question on the left simply counts the number of ways this may be done. Hence it also counts the number of ways in which the power of this term may be produced by adding n numbers or fewer, i.e. the number of ways to decompose r into n 'identical boxes' or fewer.

(continued)

>>7991016

>>7996087
Although apparently similar, partition functions [math]p_{\le n}(r)[/math] can be quite different from factorials and binomial coefficients in practice. [math]p_{\le n}(r)[/math] usually has a distinctly 'awkward' closed form, and it is usually arrived at via solving a recurrence relation that it satisfies.

As an example, we shall try to solve for [math]p_{\le 3}(r)[/math]. We can, in fact, demonstrate quite easily that [math]p_{\le n}(r) = p_{\le n-1}(r) + p_{\le n}(r-n)[/math]. This is clear if we imagine all the possible ways of partitioning r being separated into two mutually exclusive sets, the first containing all the ways of partitioning r into n-1 parts or fewer, and the second containing all the ways of partitioning r into exactly n parts. The first is easily seen to be counted by [math]p_{\le n-1}(r)[/math] while the partitions in the second set effectively force one object into each of the n parts first to guarantee n non-zero parts, so that r-n remaining objects are left behind free to be distributed in the number of ways you'd partition r-n objects into n parts or less. This second set therefore has [math]p_{\le n}(r-n)[/math] elements.

While I have not personally solved this recurrence relation, OEIS gives [eqn]p_{\le 3}(r) =\frac{(r+1)(r+5)}{12} + \frac{(-1)^r}{8} + \frac{17}{72}+\frac{2}{9} \cos \left(\frac{2\pi r}{3}\right)[/eqn]for the case of n = 3. As weird as this formula is, it can be simplified considerably by observing that the last three terms collectively amount to something within the range of [-1/9, 7/12], and so we can write [eqn]p_{\le 3}(r) = \left[ \frac{(n+3)^2}{12} \right][/eqn]where [ · ] is the nearest integer function. Hopefully this serves as a sufficiently simple general formula that appeals to you.

(continued)

>>7991016

>>7996087
>>7996089
OEIS has solutions for other n as well, which you can find at http://oeis.org/A026820. As for d) I'm not quite sure myself how I'd deal with it but this post probably gives you an idea of what's in store for you if you decide to go for solving it. Chances are it will require something more elaborate than what I've outlined here. If sufficiently desperate, you can always try brute forcing the first few terms and feeding those numbers into OEIS to see if someone has already done the work for you.

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How would i go about this?
I thought i could use the ratio or root test and then factor out x and see if the series converges or diverges for a certain x.
But i am not certain how to go on from there and determine all x that make the series converge.

>>7996246
I'm doing (a) for you, the others should work similarly.
ratiotest gives
[math]\lim_k \frac{k^2+4}{(k+1)^2+4}|x|<1 [/math]
for absolute convergence, so |x|<1. for |x|>1 it would diverge. Now we check out the rest of the points:
x = 1:
we know that the sum over 1/k^2 converges, so it converges there as well
x = -1:
you have an alternating series with vanishing coeficients, so it converges as well.

>>7996293
Alright that makes sense to me,thanks a lot anon.

Does a spectrophotometer give you the extinction coefficient or do you need to still work it out? Doesn't a spectrophotometer tell you the absorptivy (which is the extinction coefficient)?

if i pull the sound slider for example on youtube from half to maximum, does the actual sound become twice as loud or ten times as loud?

or, to phrase it differently, did google account for how our hearing works and adjust those sliders accordingly or do they represent real volume values?

>>7995628
It was intended to be done without a calculator.

Does the wave function collapse?

>>7996449
No,"collapse" is just a buzzword physicists use to say that the wave function is determined (picked out from a set of possible wave functions) at the moment of measurement.

>>7994942
I found out my headaches were caused by coffee.

>>7980526
I believe two contradictory things.

1) The integral of e^[f(x)] is always e^[f(x)] / f'(x).
2) The Gaussian Integral can't be found so simply.
Can anyone explain why I believe #1? Despite it seemingly being false, I don't recall it even failing me.

>>7996501
Try differentiating e^[f(x)] / f'(x) then tell us what you get.

>>7995147
F and G are the symbols for the fucntions. While, F(x) and G(x) are the images of x under the maps F and G.

Formally, you would write F != G.

>>7996501
The derivative of [math]\displaystyle \frac{e^{f(x)}}{f'(x)}[/math] is [math]\displaystyle \left( 1-\frac{f''(x)}{f'(x)^2} \right) e^{f(x)}[/math] not [math]e^{f(x)}[/math].

>>7996509
Fair play, it's clearly false - so why do I believe it? I know for certain that it's never failed me for anything nice like sins or cosines.

I have to find the ratio N2/N1 for an optical transition λ = 600 nm at room temperature T = 300 K which is a pretty straight forward problem but I'm getting real fucked up answers. Anyone able to help me through the method?

>>7996090
>>7996089
>>7996087
Thanks, I seem to have missed generation functions for partitions while going thru the book.

Whats the packing fraction for random packed jelly beans?

>>7996521
>noko
That's fucking retro.

Hello, I'm currently studying for some scholarship exams (Math, Phy, Chem) that take place in june 16~20.

As for Math, I'm studying number theory from Serge Lang's Basic Mathematics, and went through stewart's pre-calculus book (but I think I may be going over it again since I didn't master it completely yet).
The thing is, I'm having some trouble deciding on books to improve even more on pre-calculus and to get a basic knowledge on Calculus (I need to be able to differentiate, integrate and find maxima and minima, not that hard)
I was thinking about buying Quick Calculus: A self teaching guide By Kleppner&Ramsey (http://www.amazon.com/Quick-Calculu...rue&ref_=ox_sc_act_title_2&smid=ATVPDKIKX0DER)
Because the test only needs a basic knowledge of Calculus and I've got so little time. Any advice on this? And is there a better book on pre-calculus than stewart's?
(These are some example math exams from 2014 and 2015 exams: https://www.dropbox.com/sh/1j6f4rplsv3b33h/AADv1SM3kbGWk4r3_IJbDrXFa?dl=0)

And as for physics, I'm currently studying and taking notes from Walter Lewin's MIT lectures. And doing some exercises on the Sears & Zemansky University Physics book I purchased.
(Physics 2014/2015 exams: https://www.dropbox.com/sh/txqv20qwguyn33z/AAByidzZS8onloqYwk38rJBma?dl=0)


So, is my approach correct? Or should I attempt to change it? What is your opinion?

Thank you for reading this wall of text, I appreciate any help or advice you would give me.

Geologi or biotech?

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>>7996444
Oh okay, this is how I'd do it then.

I'm in high school and want to get a head start on Calculus for next year. What is the best resource to use to learn Differential Calc?