/sqt/ - Stupid Question Thread: Truth Edition

I am taking a lot of time travelling to college and back.
How do I learn to study in my room?
Is there a guide to follow?

>>8763893
Discourse with people I consider peers.
Listening to other people that have great authority in their field.

>>8763893
>What methods other than the scientific method do people on /sci/ find useful to gather truths in various aspects of life?

You'd get mad if you were to use the scientific method in real life to find "truths".

You can of course do experiments and find stuff, but the truth of it would be so weak it's totally irrelevant, the world is way too vast to use the scientific method in a non retarded way as an individual.

If one is interested in math, physics, computer science/engineering, what would be the best major?

I'm inclined to say physics, since it's kind of a happy medium. Can a physicist take on a mathematicians job (data analysis, actuary, etc)? And could I get into grad school for PhD if I took a few CS classes in addition?

>>8764030
*grad school for machine learning, kekkity

>>8764030
> math, physics, computer science/engineering

engineering physics is another good option If you want these subjects together

Can someone give me a quick rundown on sinh and cosh? Like what are they and what do I need to know about them? Also is there a unit circle equivalent for it?

>>8764030
Applied math could be a good choice too but you have to be careful in picking a course with good curriculum.

How were complex exponents figured out? I understand that (2^i)^i must = 1/2, but how do you work backwards from there to figure out what 2^i is and the process that leads to it?

>>8764207
2^i
= exp(log 2^i)
= exp(i log 2)
= cos(log 2)+i*sin(log 2)

>>8764207
Euler is the first to define complex exponential in his famous identity. Everything else is derived from there as shown here: >>8764215

File: Screen Shot 2017-03-20 at 5.01.10 PM.png (51KB, 516x552px) Image search: [Google]

51KB, 516x552px

I'm getting 1+(1/2^n) not 1-(1/2^n)
n is going to infinity in this so it gives the same answer - is this a typo or am I missing something somewhere? Driving me crazy

>>8764551
S_n
=2S_n - S_n
=1+1/2+...+1/(2^{n-1}) - (1/2 + 1/4 ... + 1/2^n)
= 1 - 1/2^n

>>8764564
I just realized...Sn has a 1/(2^(n-1)) term as well
fuckin derp, thanks lol

I live in the south hemisphere of the planet, it is 20:19 right now and I see a really bright thing in the sky, could it be a planet? It is much brighter than the other stars.

File: IMG_20170320_195927.jpg (111KB, 960x830px) Image search: [Google]

111KB, 960x830px

I'm so sorry for asking such a stupid question but I can't figure this out I'm an old fuck who just returned to school and all this is making me want to kms

>>8764693
>what have you tried?

>>8764693
Google the height of the Washington monument lol

>>8764693
If your being serious the answer is soh Cah toa

File: what the fuck is this.png (57KB, 784x521px) Image search: [Google]

57KB, 784x521px

senpai help this brainlet understand the functional equation part

afaik functional equation = functional programming?

so like

G(s)G(t) == G(G(t)) ???

>>8764707

oh and its a proof for "memorylessness" in statistics.

why do people continue to suppress the truth? you can't keep it hidden forever

https://www.youtube.com/watch?v=13Oa8DWpb-c

we're waking up, you're running out of time

>>8764707
>afaik functional equation = functional programming?
no not at all

functional equation just relates a function at two different values

G(s)G(t) is the product of G(s) and G(t) (your normal multiplication)

Does carbon monoxide fall or rise and why?

>>8764693
u kno pythagoras theorem? ayye

>>8764716

https://en.wikipedia.org/wiki/Memorylessness

soo uhmm its like one of those group right?

anyways,

where did they get

G(2) = G(1)^2
G(1/2)=G(1)^(1/2)

>>8764747
>soo uhmm its like one of those group right?
what?

>where did they get

>G(2) = G(1)^2
>G(1/2)=G(1)^(1/2)
by the functional equation
G(2)=G(1+1)=G(1)G(1)=G(1)^2
G(1)=G(1/2+1/2)=G(1/2)G(1/2)=G(1/2)^2 which implies G(1/2)=G(1)^(1/2)

>>8764757

does functional equation really have no formal definitions? axioms??

https://en.wikipedia.org/wiki/Functional_equation

>>8764768
>any equation that specifies a function in implicit form

File: autodiact.jpg (21KB, 480x306px) Image search: [Google]

21KB, 480x306px

how do I autodidact like a boss? book suggestions?

Is mathematica actually worth getting decent at? Been using it about a month with a c/matlab background, and I fucking hate its syntax and how unintuitive it is to write.

I picked it up originally because of the symbolic package but I could just get a symbolic package in octave and be done with it.

>>8764030
This is exactly my case
I'm gonna do Computer Engineering with Electrical Engineering focus and minor in Materials Science
I'm probably gonna do either a PhD in Materials Science or Condensed Matter Physics
Just depends what part of Physics you like
Like another anon said, Engineering Physics, by IT'S hard to sell yourself as an Engineering Physicist

What is it called when you get the nth root of the product of n values? Like square root of x * y, cube root of x * y * z, etc.

An average, but with a product instead of a sum.

>>8764974
https://en.wikipedia.org/wiki/Geometric_mean

File: image.gif (1KB, 192x192px) Image search: [Google]

1KB, 192x192px

>>8763893
So the Pythagorean theorem describes the ratio between a right triangle's sides and its hypotenuse
And irrational numbers are numbers that cannot be expressed as a ratio
Doesn't this mean that isosceles right triangles can't exist

>>8764693
756tan(36)

>>8765274
No it describes the *relationship* between sides and hypotenuse, not the ratio

Can anyone recommend me a book / tut on sum perturbation and other sum evaluation techniques? I'm having a hard time with it.

File: IMG_0661.png (39KB, 766x514px) Image search: [Google]

39KB, 766x514px

How difficult is a microbiology major? Does it depend on the uni?
Does it also rely on mainly memorising factoids and systems like with the rest of biology?

>>8765274
>irrational numbers are numbers that cannot be expressed as a ratio
irrational numbers cannot be expressed as a ratio of two integers, pi is irrational and by definition is the ratio of circumference to diameter

>>8764888
Just read on a subject. Workbooks are best because they're designed to teach. I've been teaching myself Japanese (though I'm lazy and recently started neglecting my study 馬鹿アメリカ人) though I learned enough to read and write non-kanji (with some kanji) and have very basic conversations.

File: what the fuck.png (8KB, 482x39px) Image search: [Google]

8KB, 482x39px

So I looked up some proofs on this, and they're all batshit 20 pages long. No way that they're asking for that here. Poincare-Bendixson looks tough as fuck, anything else I could use?

File: file.png (33KB, 755x173px) Image search: [Google]

33KB, 755x173px

>>8763893
I do not understand what to act the commutator on in this case, or whether it doesn't really matter and I can just evaluate [E^,PI^]B where B is arbitrary and I can divide back by B at the end.

>>8765652
Isn't that just [x,h*p]?
Anyway, B is arbitrary.

>>8765656
if something is between minus infinity and infinity is it a real number?

Also so then -i * d/dE * B would equal 0 as B has no E component?

>>8765670
Those are operators, not numbers.
The smaller infinity just makes sure some important properties hold true.

Well, yes, but this is a different context.
You want to calculate [x,p]B(x), with B being a function in some Hilbertspace, L2 or whatever. So
[x,p]B = (xp-px)B = (x i d/dx - i d/dx x)B
= ix d/dx B - iB (d/dx x) - ix (d/dx B)
= ix d/dx B - iB - ix d/dx B
= -iB
Therefore [x,p] = -i

File: images.jpg (8KB, 302x167px) Image search: [Google]

8KB, 302x167px

I'm having trouble understanding circuits, particularly voltage. So my question is more of a conceptual dilemma. Voltage is the energy provided per charge, and this energy is converted KE once the circuit is closed, or in other words it influences the velocity of the electrons, and in effect influences the current.

Pic related, as the electrons pass through a resistor, the voltage drops to 0, or the energy provided by the battery is all dissipated. Then why is the current still constant? If the voltage drops, doesn't that imply a drop in velocity of the electrons? So shouldn't it lead to a decrease in current as it leaves the resistor?

A follow up question is, why is the voltage drop the same in a resistor as the voltage provided by battery? How does a resistor "know" that it should use up the same amount of voltage provided by the battery?

>>8765687
Where does the middle term - iB (d/dx x) come from?

>>8765716
i(d/dx x)B = i d/dx (x*B) = iB d/dx x + ix d/dx B

File: e83174dddb954cefb1af3d1f196661ac.jpg (132KB, 750x655px) Image search: [Google]

132KB, 750x655px

>>8765719
Woah thank you anon you just made it all click.

Thank you very much. Have a good day.

File: WnlXYfY.png (29KB, 589x93px) Image search: [Google]

29KB, 589x93px

>Include a program listing

Meaning I include the matlab code I used, right?

>tfw pure math student who took a course that assumes all students know matlab

hehe kms

File: Lift, normal, axial relationship.png (41KB, 440x376px) Image search: [Google]

41KB, 440x376px

Can anyone help me derive the formulas shown in the pic please?

I need some good instrumental study music for math/ physics related work. Does anyone have any suggestions?

File: Capture.png (11KB, 449x97px) Image search: [Google]

11KB, 449x97px

Could someone explain me the reasoning behind the highlighted changes I see?
I am trying to solve it myself, but I guess my current knowledge only gets me this far.

Why don't car engines use some sort of heat capturing device to generate electricity? Steam turbine/Sterling engine, or something similar?

>>8765788
-a/(3^[n+1])+b/(3^[n+2]) =
-3a/(3^[n+2])-(-b)/(3^[n+2]) =
(-3a-b)/(3^[n+2])

File: cover.jpg (226KB, 1280x1280px) Image search: [Google]

226KB, 1280x1280px

>>8765740
https://modernarecords.bandcamp.com/album/ichiru

>>8765409
Irrational numbers can be expressed by any ratio of any rational numbers

>>8765906
Can't

>>8765906
>any ratio of any rational numbers
That's redundant since any ratio of rational numbers is numerically equal to a ratio of integers, as follows:

(a/b) / (c/d) = (ad)/(bc)

going over my old physics stuff again

book states "charge on an electron = 1.6x10^-19 C"

shouldn't it be -1.6x10^-19 C?
Does a proton carry -1.6x10^-19 C instead?

File: hqdefault.jpg (23KB, 480x360px) Image search: [Google]

23KB, 480x360px

My mom bought the "Lenovo Miix 310", a touchscreen-notebook hybrid with
Windows 10.

Does anybody know if it comes with hand recognition software and if no, which one is good?
Maybe for word and maybe for entering stuff on the web.
I googled and found Lenovo has a program called WriteIt but I don't want to download anything for my mom that's not needed. If the thing has a million buttons, she'll go crazy and hate it. I want to give her the most gentle introduction to this world as possible, hence the handwriting need.

Also, but this is secondary, is there anything else to draw than Paint that's recommended. For drawing flowcharts etc.

>>8764888

No book suggestions, but general simple method from someone who has been self-taught most of their life and found this method to be most effective.

Take some textbooks, go right to problems at the end of each chapter, see how much you can solve, and then refer back to the text on what you can't solve. This is pretty standard for self-teaching. Never, ever compare your answers to solutions at the end of the book, always compare them to the definitions that are given. You want to be able to derive results from a given set of assumptions, not guess and check.

Be very careful about reading. I often spend more time reading than I do problem solving because reading is easier. Don't do this. It's tempting but you'll thank yourself for solving problems more than you read.

>>8766344
By convention -- yes, it should be negative
realistically -- charge signs are arbitrary and are mostly dictated by convention. it doesn't matter which is negative, as long as you keep your signs consistent.

File: 1469374588291.png (687KB, 674x441px) Image search: [Google]

687KB, 674x441px

I failed my first exam worth 20 percent of my grade in thermodynamics (53 percent on it). Next exam is worth 25, final worth 30. Do you think I can come back from this, /sci/?

It's in thermodynamics and i'm just really struggling keeping up with the content. He also makes us turn in homeworks as a group. My group all seems to "get' it and have no time for me being the weakest link. I'm kind of at a loss and been seriously pondering withdrawing the course before the deadline this Friday.

It also adds to my frustration that the professor is kind of a scatter brained lecturer, and he combines office hours with fluids so I can never go in and ask him questions because it's jam packed.

Does anybody have any advice for me? I acknowledge my study and time management is absolute shit, but I'm kind of unsure on how I can even fix something like this. I have 3 weeks (2 + spring break) to study if necessary.

I'd love to learn how to study better desu

>>8765700
What I remember is that electrical current can be seen as a water flow between two points.

The voltage would represent the difference of height between the two points, and intensity the amount of water flowing.

Voltage drop means the electrons will have less "strength", (less water pressure), but they always move at the same speed anyway (depending only on the material).

But these are years old memories, I might be saying nonsense.

File: inductor.png (36KB, 452x516px) Image search: [Google]

36KB, 452x516px

Help me please, been stuck in this one for a while, I just don't know how to get a)

I don't GET IT, somebody please give me a quick rundown on this

File: 1474262257189.png (392KB, 451x619px) Image search: [Google]

392KB, 451x619px

>>8766628

I am not entirely sure if to get it I need to apply any of the Inductor equations or do some manipulation on the resistors at the beginning, source transformation, I am just not sure, I tried it all.

The answer (according to the book) is: -12.5A

File: brainlet_problem.png (55KB, 702x546px) Image search: [Google]

55KB, 702x546px

So I'm in the linear algebra part of my DiffEQ class, and this part has me stumped. I have searched online everywhere, but it's to no avail. Also, the lecture my professor had on this didn't help at all. I know there's 10 axioms that you need to show are true to show that a given set is a subspace, but I'm not sure if that's the correct thing to do here since we are given this equation or whatever? What I think I have to do is to verify that the sum of any 2 solution is a solution, that a constant times a solution is a solution, that x(0) = 0 (e.g. plug in 0 for x1, x2, etc...), and show that the negative of any solution is a solution, but honestly I have no idea if I'm even approaching this correctly. If I could do just one problem, I'm sure I'll get the others....

>>8766653
That's it. I think numbers are not called "constants" but scalar though

File: Art_P73.jpg (18KB, 472x289px) Image search: [Google]

18KB, 472x289px

Are there any idea on how to best represent categories and functors, graphically, except for the cases where the objects are dots and the morphisms are drawn as arrows?
Think of 2-categories where we want to make relationships clear and e.g. we want to show different depths at once

>>8766541
People do bounce back from very poor starts to a course, although not very often in my experience.

If office hours are too crowded for you to get the amount of help you need, there are other ways you can contact your professor. You can make an appointment to meet him outside of office hours. You can ask questions before/after class, or via e-mail if they're short.

If the professor is truly unintelligible you can find alternative resources; use the textbook (or another textbook if you don't like this one), find a lecture series online, etc.

Time management skills are a simple and obvious thing to fix, it's just that nobody wants to because being responsible is boring.

As for concrete steps, one thing you should do is go thoroughly through your first test and understand everywhere you fucked up. This is no fun for anybody but it's the best way to improve.

Studying for math/physics is bashing problems out. Unlike in a history course, you are tested very little on what the textbook or your notes say; you're tested on your ability to solve problems. Once you have a basic understanding of definitions and key formulas, only practice is worthwhile.

>>8766646
>>8766646

Alright so if I understood the question right. At t = 0 the switch opens. Therefore you have to calculate the conditions that are before t i.e. t < 0 when the switch is on.

You'll need phase equations (jw) to get initial states. The equations would be (for three knots):

R1 = 3
R2 = 30
R3 = 6
L1 = 8
R4 = 2

1. knot: U = I1*(R1+R2) - I2*(R2)
2. knot: 0 = I2*(R2+R3+jwL) - I1*R2
3. knot: is ignored because R4 is short-circuited by L so the current doesn't flow through it

Equate I1 as I2, plug it in and you should be able to get I2.That's your initial value of i.

>>8766682
Alright. I think that's a good place to start. I think I'll crack the whip and work on it

Do you have any tips on how to go through mistakes and gain understanding? I do that on review and always think I get it, only for me to realize I don't get it when it counts

>>8765700

Voltage (between two points) is the cost in energy (work done) required to move a unit of positive charge from the more negative point (lower potential) to the more positive point (higher potential).

When the voltage is 0 that simply means there is equal potential throughout the circuit. When you connect a resistor to a battery the voltage on the resistor will be 9V and electricity will run from the + pole, through the resistor and finally end at - pole. Gradually the battery loses it's energy (i.e. the potential is getting more and more equal) so the voltage will begin to drop on the resistor until it reaches 0. U = I/R

The resistor can't use more than 9 volts because of the law of energy conservation. The total energy in the system is 9 volts.

>>8766847

U = I*R, fucked up a little bit sorry.

>>8766646

who is this akarin impostor?

>>8764771
>implicit form

okay, how does that work?

what exactly is G(x) = ???

File: linear-congruence.png (35KB, 689x178px) Image search: [Google]

35KB, 689x178px

How do I setup the Linear Congruence for this problem?

Does anything actually care whether or not a number works as a prime number in the complex plane?

>>8767464
elaborate on 'works as a prime number'

>>8767494
Cannot be factored into real integers nor Gaussian integers

Are surfaces always 2 dimensional objects in 3 dimensional space? Wikipedia says spheres for example are 2 dimensional surfaces in 3d space, but I don't understand why. Is it just because it doesn't have any "thickness" to it? Like it's a warped section of a plane?
But if you were to parametrize a sphere why wouldn't you need 3 parameters since you're still moving in 3 directions?

>>8767574
Yes surfaces are always 2-dimensional, but the definition of "dimension" may vary. Also they do not have to be embedded in 3-dim. space.


For instance, what you call a Surface in Differential Geometry is 2-dimensional in the intuitive visual sense.

But for instance what you call a Surface in Algebraic Geometry (over C for simplicity), would be 4-dimensional in the intuitive visual sense.

File: 1489984645095.jpg (2MB, 3223x2417px) Image search: [Google]

2MB, 3223x2417px

What is PhD life really like? Can I research remotely sometimes? Can I work just 6 hours a day?

Hard to tell with how much people over exaggerate things.

>>8767592
>But for instance what you call a Surface in Algebraic Geometry (over C for simplicity), would be 4-dimensional in the intuitive visual sense.
except for 'Riemann surfaces' with are 2-dimensional in the intuitive visual sense

>>8767613
Ideally I could work in a coffee shop or something, and just meet up briefly to share results, does such a thing exist?

File: 1460743966682.jpg (284KB, 3949x297px) Image search: [Google]

284KB, 3949x297px

I apologize for dumb question, but I'm in my first year of maths at university.
What is this question asking of me? I'm not asking you to solve it for me, I just want to know what it means because the wording is too vague to me.
Is it asking me to show that [math]l_1[/math] is parallel to the line [math]QR[/math] and passes through point [math]P[/math]? or is it asking something else?
Thanks.

>>8767614
Yeah there tends to be confusing shit like that going on in the overlap of differential and algebraic geometry.

A Riemann Surface is a "surface" in differential geometry but a "curve" in algebraic geometry.

A K3 Surface is a "surface" in algebraic geometry but a "4-manifold" in differential geometry.

>>8767618
l1 is a line that passes through point P and is parallel to the segment QR

the equation of this line l1 is what is given

it's asking you to show that this equation does in fact describe a line with the previously mentioned characteristics

>>8767649
Ok thanks.

Is it really uncertain whether or not hyperbolic planes are infinite or did I misunderstand something?

Hey mathfags

I want to estimate how many different people visit a certain place. I count once a day. Problem is that people visit the place with various levels of regularity and I can't memorize all of them. Any ideas on how to do this?

A radio-active substance has a half-life of 80,000 years. You obtain some of this substance, how many years must pass for there to be 30% remaining?

>>8767680
Cmon nigga

Write down the equation for radioactive decay, N1=0.3N0, cancel out N0, solve for t

>>8767671
You need to get some sort of estimate at the frequency people return (and how many of them actually return at all, so you don't assume that every person counts for 3 when in reality 70% of your sample only came once).
Either by memorizing as many as you can or (if the situation permits) actually surveying a bunch.

Without a guess at how often your repeaters are coming back there's really no way to tell how much you're overcounting.

>>8767707
Thanks for replying dude. If I see 15-25 people every time but recognize 3-4 faces, does that help? For what its worth, I'm trying to estimate how many people use my gym.
My approach with ballparking how long people stay in the gym, adjusting for working hours etc gives me around 500 total, which is an okay estimation for my purposes. I'm just wondering if there's a neat mathematical way to do this. I'd estimate that half of them come every other day and the rest less, but no idea how to get more precise measurements.

File: trix.png (14KB, 657x316px) Image search: [Google]

14KB, 657x316px

Only question I can't seem to get, someone explain please?

File: 1473714665577.png (218KB, 400x520px) Image search: [Google]

218KB, 400x520px

>>8767669
This depends on what you mean by infinity. Consider two models, the "upper halfplane" and the "Poincaré disk". The first is [math]\{ z\in\mathbb{C}\ |\ \text{Im}(z)>0\}[/math], and the other [math]\{ z\in\mathbb{C}\ |\ |z|<1\}[/math]. As you may see, the upper halfplane goes infinitely far from the origin in all directions except down, whereas the Poincaré disk is bounded. Therefore, in the Euclidean sense, they can be both infinite and finite.

On the other hand, the axis [math]\{ z \in\mathbb{C}\ |\ \text{Im}(z)=0\}[/math], and the perimeter line of the Poincaré disk [math]\{ z\in\mathbb{C}\ |\ |z|=1\}[/math] are hyperbolically infinitely far from any point on the plane. This is due to the nature of the hyperbolic metric (of the considered model), and the homeomorphism of the upper halfplane and the disk taking the real axis together with the infinity point to be the boundary of the disk. This also preserves distance, and, since the real axis is infinitely far from any point on the upper halfplane, so is the perimeter from any point on the disk. If you want to interpret this somehow, consider the thing how gravity is usually visualized, a bowling ball on a rubber sheet bending it. Similarly, the center of the disk is where the ball is, and the closer you get to the boundary, the steeper the the climb up (or down) is eventually becoming essentially vertical. This follows from the hyperbolic metric, and the hyperbolic metric makes it so that the Euclidean distance may look small, but the hyperbolic distance can be long, making the disk hyperbolically infinite.

The same knid of idea applies for other planar models, too. Unless someone comes to counter this with a hyperbolically finite hyperbolic plane, they are all infinite in their own sense, regardless of their Euclidean boundedness. Does this satisfy you?

>>8767751
well why did you pick none?

Are there different types of math that have different primal axioms? If so, how different are they?

>>8767780
>Are there different types of math that have different primal axioms?
Yes https://en.wikipedia.org/wiki/Constructivism_(mathematics)

>>8763899
yeah it's called the guide to not being a little bitch

>>8764923
I'm probably gonna go physics, but gonna try my darndest to get into a ML PhD. Hopefully a physics understanding will help somehow.

>>8764585
probably - Venus is called the morning star for a reason.

>>8764717
It's less dense than N2, which is mostly what we breathe, but it's a gas and will diffuse pretty evenly without much separation.

>>8765700
You've already gotten some good answers, but I wanted to add that the diagram you're looking at isn't representative of a SINGLE electron's path, It's a common misconception that an electron will travel the entire path of a conductor. It's true that current is the time rate of change of charge, but this is a net effect of billions of billions of electrons. Most electrons will go towards the positive terminal of the battery (remember - they're negative charges so they go the opposite direction of current), but some will also go the opposite direction. However, the overall NET effect of charge dictates the current we calculate.

>>8765793
Heat capturing is not normally used because while it makes sense to save as much energy into useful work (or store it for later), other practical reasons usually put a halt to this. It's very likely that the cost of implementing this does not make the manufacturers any extra money or make their product much more attractive to potential buyers. Additionally, trying a new idea has some inherent risk because you'll never quite know what will happen when you release something at full production scale (you wouldn't make a single donut the same way you would make donuts for your entire neighborhood, for example). Unknowns usually mean you have to fix something later - which costs time, money, and possibly bad PR and lawsuits.

Also, some things do recoop the excess energy normally lost as heat. For example, hybrids will usually incorporate a generator into their braking system rather than the standard friction method of slowing done.

>>8767613
>>8767617
Not exaggerating - but 6 hours/day from home won't cut it in STEM. I would spend ~10 hr/day, normally, in lab. Writing papers can usually be done remotely, but your lab mates can be very valuable in discussing ideas before bringing them up to your boss and looking like a dumbass for a simple thing that could have been caught early.

Of course, each lab is very different and your experience (if you do this) will be unique from other grad students.

I need to use linear congruence to solve this:

The Melbourne cup is run every year on the first Tuesday in November. The US presidential
elections are held every four years on the day after the first Monday in November. George W.
Bush was elected on Tuesday 7 November 2000 and “Brew” won the Melbourne cup the same day.
Looking into the future, find the next date on which there will be a US presidential election
but no Melbourne cup.

Any ideas?

Can some explain interuniversal teichmuller theory to me?

File: 1489051894550.jpg (38KB, 549x673px) Image search: [Google]

38KB, 549x673px

>>8767988
https://www.maths.nottingham.ac.uk/personal/ibf/notesoniut.pdf

>>8767988
No, it requires a certain IQ level to understand and you just aren't there, sorry

>>8768009
Can you give me a quick rundown on this guy

How do I load a custom webpage onto chrome for the New Tab/ New Window page?

>>8767751
Just calculate every possibility. But it's strange the scaling and translation are given by 2D vector when the matrix is 3*3

>>8767985

If I were you I would start saying all years have the same numbers of days

Then you can express the dates you're looking for as a certain congruence (depending on the number of years passed from 2008 e.g.)

Any neurobiology or psychology majors help me figure out more precisely what stress is from a more philosophical perspective?

Like is stress only a response to perceived life-threatening events or like it's just a switch that's flipped on or off, or is it like a spectrum.

If say, I'm really really really horny, or in a state of mania, is that stress causing that or is stress exclusive to negative emotions like anger and fear?

File: linear_congruence.png (35KB, 686x177px) Image search: [Google]

35KB, 686x177px

Solve this problem and post your bank deets for a small reward

File: linear-conngg.png (18KB, 681x169px) Image search: [Google]

18KB, 681x169px

Any ideas on how to solve this?

>>8768404
sent ;)

File: twog.jpg (34KB, 640x480px) Image search: [Google]

34KB, 640x480px

How does the resulting graph look like when you add these two gauss curves? (I asked this already some weeks ago but I asked it quite late in the thread so the thread died before I got an answer)

>>8767926
>>8764717
that's a dangerous answer
it doesnt mix so easily when there is little air swirling, so it tends to sink to the ground and people suffocate in their sleep

>>8768255
there is more than one definition of stress, there is emotional stress and there is cellular stress, and others

File: Untitled-1.png (19KB, 576x357px) Image search: [Google]

19KB, 576x357px

>>8768426
Means: 1 and 2
SD: 1
Protip: you can do shit like this online all by yourself

>>8768444
thx a lot, but where? at wolfram alpha?

What is "β" in regards to the Schrodinger equation in the case of a potential step? "β" hasn't even appeared once in the lecture notes and I can't find anything relevant about it on google. Here is the question (I know how to do everything except for finding β):

"From the solution of the time independent Schrödinger equation, write down an expression for the wavefunction of a 0.5 eV electron moving from the left (x<0) and interacting with a 1eV step potential at x=0. Calculate k and β."

>>8768430
Gas stratification does happen when there's a lack of convection, but again, it's less dense and will tend to separate to the TOP layer, not sink to the bottom. Carbon monoxide poisoning is lethal and happens at very small concentrations, even without stratification of gases.

>>8768432
I prefer von Mises, myself.

How do I calculate the simultaneous confidence level of two confidence intervals? For some reason I'm having trouble finding a straight answer with google.

How do you do linear regression if each x-value has multiple y-values?

>>8768722
BUMP

>>8768407
For each prime p, find the highest power of p that occurs in any of the [math] n_i [/math]. Equivalently, take their least common multiple.

1 mod 6
1 mod 20
is equivalent to
1 mod 4
1 mod 3
1 mod 5
is equivalent to
1 mod 60

File: springschedule.png (9KB, 368x292px) Image search: [Google]

9KB, 368x292px

How hard will this 12 week semester be?

>>8769284
I refuse to look up these courses; what are they?

Could anyone here help with matlab?

File: Classic-Ukrainian-Borsch-5-600x400.jpg (52KB, 600x400px) Image search: [Google]

52KB, 600x400px

>>8769368
don't ask to ask brainlet, just write out a specific question

File: me settis.png (6KB, 366x298px) Image search: [Google]

6KB, 366x298px

>>8769396
Fair enough.

I have this piece of shit going (and somehow it seems to be running fine). How would I add 2 sets of initial values that will be solved by ode45?

Would all my atoms explode if I walked into hyperbolic space? Asking for a friend.

>>8768722
Linear least squares regression doesn't care that you have several values for a given x. Maybe the tool you're using for linear regression is shitty and doesn't let you have multiple values for a given x, in which case, use another tool, otherwise just go ahead and write each pair of (x,y) value without being concerned by the fact that some of these x's are equal.

>>8769534
Yes, but what does the matrix vector equation look like?

>>8769538
I'm not sure what your problem is. Which particular step that you do when all x's are distinct poses you a problem when some x's are equal? There should be basically no difference at all.

Say you have 4 values:
x=0, y=-1
x=0, y=1
x=1, y=1
x=3, y=3

Your x vector would be (0,0,1,3), your y vector would be (-1,1,1,3), and you'd be looking to solve y=(a,a,a,a)+(b,b,b,b).x+e for a, b and e in such a way that the L2 norm of e is minimized.

>>8769566
Ah right I see it! Thank you.

File: water-1246527_960_720.jpg (362KB, 960x720px) Image search: [Google]

362KB, 960x720px

is double majoring in physics & EE a good idea? I'm not sure I want to go into grad school, so I think tacking on the EE would help with jobs.

I mean, ideally I'd major in math, minor in philosophy or physics and read poetry all day but hey I gotta eat

today I took 400mg of modafinil and felt almost nothing. Does this mean my dopamine system is a bit fucked? I am very depressed and am wondering if this is the neurological cause

>>8769573
if you're depressed, try shroomies in a serene setting m8 :-)

nothing nicer than chilling in the woods on shrooms, you don't even have to take a big dose to enjoy either

>>8769570
You're welcome.

>>8769577
i probably will at some point in the future because i have reached a point where i figure my mind is in a bad enough state that there's very little at risk. But does my theory of it reflecting badly on my dopamine system's performance make sense?

File: brainlet.png (71KB, 775x307px) Image search: [Google]

71KB, 775x307px

>>8769605
I don't know enough to comment on it, but my inclinations would tell me that's a possibility, but I have never even heard of the medicine, so I don't know it's intended effects, or how the body processes and utilizes it.

>>8763893
Pls help a brainlet out with pic related, /sci/. I don't understand the last step where the denominator becomes 2^(n+1). How would I intuitively arrive at that point?

>>8769620
pls halp, this should just be a basic algebra question

>>8769407
>still naming functions with "my"
oy vey

>>8769620
[math](\frac{-x}{2})^n = (-x)^n(\frac{1}{2})^n[/math]

then you multiply everything by 1/2 so the 1/2 term goes up to n+1

>>8769620
theres the 2^n already inside the sum
[since (-x/2)^n=(-1)^n x^n (1/2)^n]

and the 1/2 outside the sum

so (1/2)(1/2)^n=(1/2)^(n+1)

>>8769676
>>8769677
ty, after watching a few elementary videos on powers I began to realize but the confirmation is useful

nothing like watching videos intended for 7 year olds as I prepare for a multi variable calc final

File: Engineering.png (24KB, 640x480px) Image search: [Google]

24KB, 640x480px

Did I just divide twice by accident? or does dividing both sides by (140,000/190,000)^2 actually give me the acceleration at the surface and I'm just retarded.

>>8768012
hes pretty good at math.

File: 18-726s09.jpg (14KB, 320x320px) Image search: [Google]

14KB, 320x320px

>>8763893
I just finish Geometry in khan academy , is that enough to start study euclidean geometry?
with poor base in trigonometry

Why is (2^(K+1)-1)+(2^(K+1)) = 2^(K+2)-1

What is the rule for adding 2^(K+1) + 2^(K+1) -- and in general what kind of addition is this?

Thanks from a brainlet

>>8769862
2^k+2^k=2(2^k)=2^(k+1)

>>8769865
Help me understand the last part 2(2^K) you aren't saying 4^K which is what I wanted to do. Help me see it correctly

>>8769865
Also why would it be 2^(k+2) when you add 2^k + 2^k

>>8768407
X=1 and x=lcm(the n's)+1

Assuming none of the n's is 1

Given a relatively well supplied home biology lab, is there anything one could do in it for fun and (ideally) profit? Found a website that sells PCR/CRISPR kits for a nearly affordable price; just wondering if there's something I could do to make up for the loss of money. Thanks /sci/

>>8769874
>>8769889
Brainlet here as well, but i think we are just using factorization here.

I know nothing about astronomy. What are some good introductory texts for someone who wants a from the very beginning history of astronomy book? I already have my own list of links and books but I want to see how recommendations compare. Thank you.

>>8769347

Microeconomics, Women Studies: Chicano/Latino contemporary issues, Organizational Behavior, Philosophy: Current Debate about sexuality, Statistics.

>>8769926
I think I figured it out (original brainlet here)

2^k + 2^k = 2*(2^k) = 2^1 * 2^(k) = 2^(k+1)

similarly for my original question,

2^(k+1) - 1 + 2^(k+1) = 2*(2^k+1) - 1 = (2^1 * 2^k+1) - 1 = 2^(k+1) - 1

>>8770045
Brainlet from above here.
Are you working on sequences ? I'm trying to get into this as well. I find it very confusing compared to the other chapters that i have been learning like integration and vectors.

WHY ARE THERE STILL MOSQUITOES IN 2017

>>8764693
Tan(angle) = opposite/ adjacent
Tan (36) = h/765
H = 765*tan (36)

Also
>feeling sorry for asking a stupid question in a stupid question thread

File: ladder.jpg (64KB, 1000x696px) Image search: [Google]

64KB, 1000x696px

Brainlet problem pls no bully. The answer for Rb is supposed to be 122.6N. Am I missing something or is it simply because of rounding errors?

Not really a question but,
Does anyone have recommendations for decent, cheap, portable laptop to do school work on. that can run things like matlab, python, Mathematica, etc?

Give an example of a function whose domain is
the set of real numbers and whose range is not an
interval.

>>8770217
I think because the vertical wall is "smooth" it is not supposed to have a reaction in the vertical direction. Try modifying with Rb being completely horizontal.

>>8770548
You mean like y=a? (where a is any real number) The domain is all of x. The range is just a

>>8770548
f: R->R
f(x) = 0 if x is irrational
f(x) = p, if x is rational in the form q/p where q,p have no common factors

Many similar examples exist. This is easy to visualize, but the Stars Over Babylon function is a more typical example: this function is the same as what I wrote but f(x) = 1/p if x is rational

>>8770559
a single number is an interval. An interval is just a connected subset of R

>>8770560
>f(x) = 0 if x is irrational

Isn't 0 in the interval [0]? Also thanks.

>>8770567
Yes, of course each individual output is itself an interval, but you asked if the range is an interval. Specifically, the range is the set of all integers, and also 0. Therefore it isn't an interval.

It's impossible to have a function whose individual outputs aren't intervals, since every real number is an interval by itself. This is definitely not the intention of the problem though

>>8766446
Guessing and checking as a crutch is bad, but I disagree with looking at answers. The semi famous experiment where that guy at MIT learned an entire CS undergrad curriculum in like 6 months has a very detailed writeup on the best strategies for autodictatism, and one of the most important three principles he emphasized was being able to get immediate feedback. He was so convinced of this that he basically dismissed trying to learn from any material you don't have at least short solutions to, if not detailed solutions with notes. It simply is an order of magnitude less efficient.

You have to be disciplined: don't scribble something and then turn to the back, make sure you have some justification for your answer, reason through your progress, then check.

>>8766653
Protip: while a vector space has 8 (10?) axioms, to show that something is a subspace, you merely need to show that it

1) is closed under addition
2) closed under scalar multiplication
and
3) contains the zero element

this is because all remaining axioms are "inherited" from the larger vector space: they are true in any subset. So you only need to demonstrate that the above three noninherited axioms hold

>>8766653
>>8770585
In particular, your example IS a subspace. This is easy to show formally with some quick algebra, but you can also see that it is intuitively: if the x-y plane is horizontal, the 3x1 - 2x2 = 0 is simply the line y = 3/2 x. Now z is unconstrained, so you have this line extended vertically in both directions to form a plane. Voila, your set is a plane containing the origin: it is clear visually that any vector on this plane, when added to another, results in a third vector still on the plane. Analogously so for multiplying any vector by a scalar

>>8765605
Lienard's theorem

when does someone stop being a brainlet? is it when they pass Calc 1 or Calc 2?

brainlet asking, Third time trying precalc, I know the unit circle full and through, Its domains ranges that screw me over. I wanna learn the maths, but I'm a fucking retard of a brainlet.

My plan is to learn something in science, current plan is to transfer to Illinois state uni, no fucking Idea what I want to go into Just something in science

Damn it is really fun to go through these at 200 replies and make sure I can answer all the questions

I missed three questions this time around

>>8770573
>Yes, of course each individual output is itself an interval, but you asked if the range is an interval. Specifically, the range is the set of all integers, and also 0. Therefore it isn't an interval.

Range is the image right? So if it is the set of all integers and 0, i can write it as an interval.

The book i got this question doesn't talk about codomains and sorry if i'm being too dumb

>>8770611
First lets clear something up, because there is ambiguity. Codomain is a name for the set that a function "makes sense" to map into. For a real valued function, the codomain is the set of real numbers, even if the function doesn't have an output at each real number.

The image is precisely the set of outputs of the function. for f:R -> R like we are talking about, the codomain is R, and the image is y in R such that y = f(x) for some x in the domain (also R).

The word range is a cancerous abomination of mathematics that is used interchangeably to mean image or codomain. Lately it has been used moreso to mean image, so usually you should assume that's what it means though

Now the image of the function I gave is 0,1,2,3,4,....... etc, while the codomain is still R. Intervals as a concept in R are like I said connected subsets of R: what this means to you is that they are bounded on each end by a number, say a on the left and b on the right, and for EVERY SINGLE x in R such that x is between a and b, x is inside the interval.

So our image of 0 and the integers is very clearly not an interval: any two integers have at least one (in fact have infinite) real number between them, but this real number is not an element of the image of f.

Just try to write an interval out of the restricted image 0,1,2. [0,1] doesn't work, since 1/2 is in that interval, but our function doesn't hit 1/2 anywhere; 1/2 is not in it's image.

>>8770611
>>8770661
Even though we can write each individual output as an interval, specifically the trivial interval containing only that output, unions of intervals are in general not themselves intervals. Think of a number line. Intervals have to be everything between the endpoints--we can't "skip over" any real numbers. But our function does exactly that: it skips over ever single number that isn't an integer. So its image is only the integers, and therefore its image is not an interval. A finite set of integers could be CONTAINED in an interval, say 0,1,2,....100 could be contained in the interval [0,100], but there are all these real numbers in [0,100] that aren't in our original list.

>>8770666
>>8770661
Thanks so much!

>>8767988
>can someone explain something that builds on the majority of the history of mathematics to me in less than 2000 characters

no.

>>8770707
B-but I was told there were non brainlets here. How can you guys call yourself smart if you can't even understand IUT?

>>8770548
f(x)=x if x<0

f(x)=x+1 if x>=0

>>8765906
Brainlet... ever heard the non-terminating and non-repeating aspect of an irrational number?

Brainlet here. Not sure if this is the c orrect thread of this

I've been reading books like "Introduction to Calculus/ Fundamental Calculus / Introductory Linear Algrebar" in order to unfuck my shitty education background but sometimes I feel inadaqute in following the flow of the chapters. It feels like that I lack a certain "mathematical state of mind" or such

Will I get better by just press on doing the exercise or are there texts that I can read regarding this?

I need to use linear congruence to solve this:

The Melbourne cup is run every year on the first Tuesday in November. The US presidential
elections are held every four years on the day after the first Monday in November. George W.
Bush was elected on Tuesday 7 November 2000 and “Brew” won the Melbourne cup the same day.
Looking into the future, find the next date on which there will be a US presidential election
but no Melbourne cup.

Any ideas?

>>8771021
get a calendar lmao

>>8771021
How about, when you make a thread asking for help, you actually read the replies?
>>>/wsr/284283

>>8770995
You might want to skip ahead to see where things are going (look at the big-looking results), and then go back and read up on the details. Also, you have to spend time actually visualizing some things. Just being able to manipulate letters correctly isn't "understanding". So if your book only has exercises that want you to repeat a trick, doing the exercises isn't enough.

So it could be the case that you have a shitty book. Its rating on Amazon is generally a good indicator.

File: 319996.jpg (42KB, 225x350px) Image search: [Google]

42KB, 225x350px

Hello /sci/! Brainlet here !
I got a stupid questions:
Okey so i live with a random guy and he forgot to lock the door to the bathroom while he was doing his thing today and i walked in on him. He got angry and yelled at me even if i closed my eyes and ran out really fast. What could i have done different ? Who's fault was it?

>>8771166
oh it's a meme lol

>>8767464
I don't know, but understanding simple cases is a stepping stone to more important results in algebraic number theory.

>>8770607
so you know maths and nothing else? impressive.

>>8771186
some people are irrational and think theyre always right. just ignore the egotistic kid and study/focus on projects moar.

>>8771186
His.


Lock the fucking bathroom door.

>>8771186
>closed my eyes and ran out really fast

What are you, some kind of faggot? You should have yelled back, got into a fist fight, then made out with him on the bathroom floor.

>>8771250
heh

File: IMG.jpg (192KB, 3954x1219px) Image search: [Google]

192KB, 3954x1219px

I don't even know where to fucking start

>>8771316
normalize:
Integral psi^2=1

orthogonal:
check <psi_i|psi_j> = delta_ij

>>8771316
Start by reading the definitions of "normalized" and "orthogonal".

File: V6dYjeY.jpg (497KB, 986x1200px) Image search: [Google]

497KB, 986x1200px

Show that the sum of two odd functions is an odd
function

>>8771450
literally trivial brainlet

there's nothing to even get stuck on, its one line

>>8771450
>Show that the sum of two odd functions is an odd function
1. Apply property.
2. Use math magic.
3. ????
4. Profit.

>>8771453
>>8771460

I really don't know how to do it, there is no answer in my textbook.

Is it f(-x) + g(-x) = (- f - g)(x) ? I didn't get the question.

How do I solve this equation?

[math]\sqrt{3x^{2}~-~3}~+~\sqrt{5~-~x^{2}}~=~\sqrt{4x^{2}~+~8x~+~1}~-~1[/math]

>>8771450
>>8771472
Answer this question:

What is the definition of an odd function?

>>8771480
when f(-x) is -f(x)

>>8771486
Okay, and what is the definition of the sum of two functions?
I'll answer it for you:
f+g = h where h(x)=f(x)+g(x) for all x.

Now, the question is:
If we know that f(-x)=-f(x) for all x, and g(-x)=-g(x) for all x, prove that h(-x) = -h(x) for all x.

How about you fill in what h is in that last equality.

>>8771491
So h(x) = (f+g)(x) then, h(-x)=(f+g)(-x) which is -h(x)=(-f-g)(x), so its just this?

Can genetics be altered biochemically, as in can you actually change stuff like intelligence or physiology, like height or bone structure through chemical compounds?

t. doesn't know shit about biology or chemistry

>>8771507
Yes

File: mspaint.png (17KB, 752x1808px) Image search: [Google]

17KB, 752x1808px

>>8771507
If you need to ask, you don't understand it, but yes.

h(-x) = (f+g)(-x) = f(-x)+g(-x) = -f(x)+-g(x) = -(f(x)+g(x)) = -(f+g)(x) = -h(x)

>>8771478
Short answer: Square, isolate roots, square, isolate roots. Repeat until you have no roots.

Long answer:
Sqrt[a]+Sqrt[b]=Sqrt[c]+d
a+b+2*Sqrt[ab]=c+d^2+2d*Sqrt[c]
a+b-c-d^2=-2*Sqrt[ab]+2d*Sqrt[c]
(a+b-c-d^2)^2=4ab+4cd^2-8d*Sqrt[abc]
(a+b-c-d^2)^2-4ab-4cd^2=-8d*Sqrt[abc]
((a+b-c-d^2)^2-4ab-4cd^2)^2=64abcd^2

>>8771514
>>8771513
Thanks

File: 32c2b0681813496a7cc0a921cc464afb.png (2KB, 140x96px) Image search: [Google]

2KB, 140x96px

Could anyone help me with this integral without using arcsin and arccos? i have written down something but i doubt it is correct, but i'm not able to check my answer.

>>8771539
>but i'm not able to check my answer

Why?

>>8771541
Because wolfram and symbolab uses arc to solve it. And it's outside of my pensum. I'm supposed to solve it without it.

>>8771539
I got
[math]-4\sqrt{7-x^2}+c[/math]

used u-sub where [math] u = 7-x^2[/math]

>>8771539
Hint: calculate the derivative of [math] \sqrt{7 - x^2} [/math].

File: Capture.png (23KB, 720x284px) Image search: [Google]

23KB, 720x284px

>>8771543

>>8771546
>>8771549
>-8*sqrt(...)
shit yeah, oops

>>8771521
Thanks.

>>8771541
>>8771546
>>8771548
>>8771549
Sorry guys, i don't know what is show'd up differently for me.

>>8771316
ok I solved it, I got that psi(a),psi(b) and psi(b),psi(c) were orthogonal

but what if I wanted to find the normalized constant, for example for psi(a), it should be 1/sqrt2, but all I get is sqrt2

is it N(a)=1/(sqrt(|psi(1)|^2+|psi(2)|^2)?

File: matlab.png (31KB, 622x299px) Image search: [Google]

31KB, 622x299px

How do I plot the time steps?

>>8771608
no matter, solved that oo

i've heard that chewing food and spitting it out too often can cause ulcers. does the same thing apply to blowjobs/semen?

>>8771668
>she doesnt swallow

>>8771668
>He's trying to make a point

Godspeed, friend.

>>8771521
Wait, doesn't all that squaring give you more solutions than were in the original equation?

>>8771857
So you have to just solve some horrendous polynomial and then check all the solutions by plugging them into the original equation? Is there no way to avoid the high order polynomial?

>>8763893
I just bombed an exam in real analysis and am really depressed about it. How do i stop being a faggot and get over it. Double my efforts and get ready for the final?

File: Screen Shot 2017-03-23 at 1.10.17 PM.png (606KB, 1466x1418px) Image search: [Google]

606KB, 1466x1418px

I have a Physics (Mechanics) final in a couple of hours and I'm a brainlet. How the fuck would #4 be D?

>>8771955
That's simple. You have the weight of the pulled out drawer balancing the weight of one of the other drawers so that their total weights is on the front support (2Mg). Then half the weight of the rest of the cabinet rests on the front support (3Mg/2). So the total weight on the support is (2+3/2)Mg = 7Mg/2.

How do i calculate flow rate out of a closed system if it's pressurised to 5000 psi? Do i need to integrate bernoullis equation with time?

>>8772025
This is sort of a weak cheap answer. Relying on intuition is a bad habit

This problem is very difficult (relative to what it is now) if it isn't multiple choice. It actually becomes a torque problem at that point. Luckily for you, of the four answers, only D makes any sense:
A is the entire weight of the cabinet, which is absurd
B is half the weight of the cabinet, which is what it would be if the drawer were closed
C is less than half the weight, which would only be plausible if the drawer was extended out the other side
D is the only answer where the weight increases but isn't the entire weight of the cabinet

File: quara.png (93KB, 423x189px) Image search: [Google]

93KB, 423x189px

Can't stop laughing

>>8772086
Oh shit you're right.

I asked some people and what they wanted you to do was basically calculate the Torque about B

It would be (Torque due to the weight of the Cabinet, 4*MG * L/2 ) + (Torque due to the extended cabinet, MG * 3*L/2) - (Torque due to the normal force from the floor on F)
(L is the length of the cabinet)

So it'd be (4MG*L/2) + 3MG/2 - FxL = 0, therefore, F = (2MGL + 3MGL/2) => 7MG/2

>>8772086
>This is sort of a weak cheap answer.
No it's not; the reasoning is solid. This is how you solve problems quickly, especially for multiple choice.

[math]a+a(\sum\limits_{n=1}^{\infty}(b-ab)^n)[/math]

Did I do this right?

File: thermodynamics question.png (39KB, 794x100px) Image search: [Google]

39KB, 794x100px

am i missing something obvious, because to me it seems that it is impossible to find the answer to this without knowing the volume of air, given that enthalpy is H = U+PV

>>8772230
Looks like a conserve energy thing. Take the sum of your energy from pressure, velocity, internal temperature. Then have it equal to C, and rearrange the other side to find V as a function of this C.

if tanx = (-24/7), and x is an angle in quadrant 2, find sin (1/2)x

for all values of a for which the expressions are defined, prove the following is an identity:

cot A = (1+cos A + cos 2A)/(sin A + sin 2A)

Prove the identity: sin2x = tan x (2-2sin^2 x)

For all values of x for which the expressions are definded, prove the following is an identity:

(cos2x/sin x) + (sin2x/cos x) = cscx

What is an example of a two-to-one function
f: [a, b] -> Real numbers ?
like f inverse(y) has either exactly 2 elements, or none.

Can 1 dimensional space be hyperbolic?

Somewhat related.
I helped a friend with an assignment by showing them my work and explaining how to get to the answer.
They turned out to basically rip off my entire work and we're being accused of plagiarism.

I'm in the clear as long as I prove it was my work originally right? I shouldn't get 0 or anything?

>>8772711
Simply explain to the professor that you were trying to explain a single problem to them, and that the other student unexpectedly was dishonest and stole your whole assignment. Emphasize that your intentions were merely collaboration and that in the future you won't help this student because they are untrustworthy

>>8772593
my first thought is -cot(2pix) where you set f(0) = 0 and f(1) = 0
This should map [0,1] to R in a 2-to-1 fashion, might be a slip up though I'm drunk and it's late

Related and something that is definitely correct is that there is no continuous such function from [0,1] to R, even if it doesn't have to be 2-to-1. [0,1] is compact, R is noncompact, and continuous maps preserve compactness.

Another way to see this is that f(x) on [0,1] must have a maximum and a minimum by the Extreme Value Theorem; if it mapped to all of R, it would have neither.

>>8772734
Nah this is a bad example. It's a good answer to your question where the domain is the open interval (0,1). Since it already hits everything in R twice on this interval, there is no way to make it exactly 2-1 on [0,1], since now we have to map 0 and 1 to something

>>8772687
No, because curvature is not defined in 1 dimension.

>>8772593
Not pretty, but yeah.
[math]x=\sum_{i=-\infty}^{i=\infty}x_i\times10^i,\, \forall_i:(x_i\in \mathbb{Z},\, 0\le x_i \le 9)[/math]

[math]y=\sum_{i=-\infty}^{i=\infty}y_i\times10^i,\, \forall_i:(y_i\in \mathbb{Z},\, 0\le y_i \le 9)[/math]

[math]f(x,y)=\sum_{i=-\infty}^{i=\infty}\left( x_i\times 10^{2i}\right) +\left( y_i\times 10^{2i+1}\right)[/math]

>>8772745
But can't a 1 dimensional space form a circle just like a 2 dimensional space can form a sphere?

>>8772734
>>8772739
I just realized you probably don't even mean a surjection. You're simply asking for a two to one function.

The function [math] \sqrt{|x|} [/math] on any real interval is such a function

I told my gf that love doesnt exist and its just way to trick us for reproduction, she got really mad and doesnt want to talk to me, am i wrong?

File: tmp_578-1457921685491-1779134072.jpg (61KB, 604x438px) Image search: [Google]

61KB, 604x438px

I was planning on majoring in plant science but I find molecular and cellular bio extremely boring, it feels like too much memorization. Is it representative of biology? Thinking of switching to physics or chem

How do I know which letters I should use to represent my variables that could be represented using literally any letter?

>>8772734
>>8772739
>>8772751
These are all me, to avoid confusion.

>>8772747
There are far simpler answers for all interpretations of the question. Whether the interval is open/closed, negative/positive, the function has to be exactly 2-1, the function has to be surjective, whatever.

In any case I think he didn't mean a surjection, since he said that the the inverse image (we're talking about the inverse as multivalued) has either 2 elements or none--- if it has none, then f doesn't have to be a surjection

>>8772751
not on any interval containing 0

>>8772768
today is not a good day for me

>>8772763
Can you think of a simpler bijection? The question is trivial if he isn't even asking for a surjection. It should at least be surjective to a subset of [math]\mathbb{R}[/math]

>>8772749
It can

>>8772773
meant injective for a restricted codomain

>>8772778
So why does positive curvature work below 2D, but not negative curvature?

>>8772751
No take f inverse(0). You only get zero back. Plus if you restrict domain to positive numbers, its surjective.

>>8772782
>>8772773
I'm not sure what you mean, it can't be injective, since it is 2-1. For y in the codomain,

[math] Image^{-1} ( y ) = {x_1, x_2} or {} [/math]

>>8772787
Latex:

[math] Im^{-1}(y) = \{x_1,x_2\} \quad or \quad \{\} [/math]

>>8772787
1/abs(x)
?
Dont think this works bc f is not defined on 0

>>8772787
I interpreted it to mean f: one ordered pair => one real and f^(-1): one real => one ordered pair. It's still possible to have an injection like this, but I personally didn't think of anything simpler than what I wrote the first time >>8772747

>>8772783
It doesn't work at all, there's just nowhere to curve into in 1 dimension

>>8772797
Inverse image as a set, not ordered pair.

2 distinct elements in the domain map to a single element in codomain.

>tfw brainlet

how do i deal with the factorial in the ln? I think i'm supposed to use ratio test (trying to test for convergence or divergence)

\sum_{k=1}^\infty \frac{ln(k!)}{k^4}

>>8772797
Dude it's a function a real valued function of one variable.

f: [a,b] --> R

It can't be an injection as stated. It's two-to-one, another word for injective is literally one-to-one. The premise of the question is that each element in the image has two exactly two elements in the preimage

>>8772807
oops

[math] \sum_{k=1}^\infty \frac{ln(k!)}{k^4} [\math]

>>8772812
delete this

[math] \sum_{k=1}^\infty \frac{ln(k!)}{k^4} [/math]

Has anyone ever had sex or bated in space?

>>8772806
>>8772809
Ah, I've never seen "two-to-one" before. I assumed that was just describing an injection R^2 => R

Is whether or not a series diverges related to the ratio between one term and the next?

>>8772815
[math]
\begin{align}
\ln(k!)&=\ln(k)+\ln(k-1)+...+\ln(2)\\
&\lt k\ln(k)\\
&\lt k^2
\end{align}
[/math]

Take it from here.

>>8772827
Check out d'Alembert's test

>>8772828
hmm thanks this is really making me think

>>8772812
>>8772815
here's how you do it:

< \sum_{k=1}^{\infty} \frac{ln(k!)}{k^4} >

You need {} around the upper limit of the sum too

>>8772812
>>8772807
>>8772842
Check out
http://quicklatex.com/
to get quick previews; never look like a fool again

File: Capture.png (6KB, 309x193px) Image search: [Google]

6KB, 309x193px

>>8772845

>>8772845
Those were all tagging fuckups and not code fuckups.

So this is kind of a personal problem
I think I have some kind of phobia of school work, like I don't think the material is necessarily hard, and I can work hard and study difficult subjects just fine in my own time, but the minute I sit down to do a graded assignment, no matter how easy, I start to get anxious, a lump forms in my throat and my chest gets heavy. I've tried breaking my assignments down and it kind of works, but eventually I get a question that's kind of hard and everything falls apart. What can I do to manage this?

>>8772860
take a shot of whiskey b4 starting ur homework

>>8772863
I'll try it but I'd prefer a solution that won't eventually turn me into an alcoholic

When do you use multiplication signs as opposed to just sticking things together? Is there anything wrong with shoving a summation in the middle of a formula? If not, does a summation need to be parenthesized?

>>8772860
Read your assignments when you get them until you understand what the hard parts are/what you have to think about

Then think about them throughout the day/week

Lets say you get psets on monday and they are due the next monday. I would probably read it monday/tuesday and then think through the questions, maybe rereading if I needed to, until friday. During this time, you should go to office hours to discuss the harder problems. You can't go to office hours if you haven't looked at the homework, so the purpose of this technique is to make you familiar enough with the problems to discuss them in office hours and hopefully get what you need to solve them right there/later (sat/sun)

Saturday you might write down the solutions you know, grind out the ones that are just going to take time and not a lot of thought, and start to really attack the hard problems--but hopefully you've made some progress on them, "parameterized" them, so you are familiar with them and they are your friends by now.

On Sunday you are taking the solutions you've written to the other problems, writing up the nice, clean document you're going to turn in, and then one by one solving the harder problems left and then transcribing/writing them up on your nice pset copy. Often if you really do this technique you will not have anything to get stuck on by Sunday (or the 6th day of your :"work week", depending on when you get your pset) because the easy problems will be pushed to Saturday and whipped out, while all the hard problems have been percolating, discussed, and solved gradually throughout the week

The worse way to do psets both for understanding and for grades is to sit down and try to do it start to finish. This results in frantic googling(first concepts and then as you become desperate, "solution pdf"), partial answers, and stress.

I know it seems like a lot of effort, but try it once or twice and really discipline yourself to do it and you'll see that it works miracles.

>>8763893
>>8772888
In addition, this method will make you understand the material infinitely better than trying to do it all at once. Just the act of thinking about math (or whatever you are studying, I study math) every day will make you markedly more proficient and able to talk about your subject.

If you have classmates that all cram last minute, they likely spend less total time per week on each assignment than you. But every single week they are adding more material to the category "things I am expected to know but don't really know" while you are adding more and more material to the category "things I am expected to know and really understand" as well as the category "things I am not expected to know but learned incidentally through my excellent study habits"

>>8772593
>>8772797
Yoo >>8772795
solved it and we didn't even realize.

Yes this is undefined for 0, and that's perfect. It isn't a surjection, but 1/abs(x) is exactly a 2-1 function on any symmetric interval [-a,a] around 0. Now we need to generalize to any interval [a,b] by shifting that interval back to one symmetric around the origin:

[math] \frac{1}{abs(x - (\frac{a+b}{2})} [/math]

>>8772906
except its not defined at (a+b)/2 brainlet

>>8771857
> doesn't all that squaring give you more solutions than were in the original equation?
Yup.
E.g. x=-2 is a solution to the degree-8 polynomial, but it isn't a solution to the original equation.

>>8771884
> So you have to just solve some horrendous polynomial
In this case, the polynomial factors to:
(x+2)^2*(x^3-2)^2=0
So you have x=-2 or x^3=2; the latter has three solutions (one real and a complex-conjugate pair). Only x=2^(1/3) is a solution to the original equation.

If you're restricted to the reals, then the terms inside the square roots must be positive.
3x^2-3>0=>x<-1 or x>1.
5-x^2>0 => -sqrt(5)<x<sqrt(5)
4x^2+8x+1>0 x<-1-sqrt(3)/2 or x>-1+sqrt(3)/2
Altogether:
-sqrt(5)<x<-1-sqrt(3)/2 or 1<x<sqrt(5)

>>8772893
That actually sounds like great advice and I'll try it out. What would you suggest for getting through long technical readings? I'm studying physics and some of the chapters I need to read are long difficult to grasp, and I find it hard to focus on reading for very long before the anxiety gets to me.

>>8772893
>>8772906
>>8772920
As I said I study math, but I've taken most of the undergraduate physics curriculum, so I have a sense of what you're talking about. It depends on what you mean:

If you are studying material, you shouldn't often be reading pages and pages consecutively. You should be examining the concepts conceptually, and summarizing long readings into the important bits. Some classes like to assign a ton of reading every lecture, and this can be a trap:

Lets say you are studying conservation laws and energy. You have 40 pages to read associated with one 75 minute lecture. The lecture might go something like this: a five minute discussion of previous topics and how they lead into this one, then an intuitive example of a "ball on a hill" followed by drawing a formal energy diagram that shows the relationship between potential and kinetic energy, and then a statement that energy is always conserved, and then progressively harder example problems with new concepts each time: one about a box sliding down a ramp in 2d, then addition of rotational energy to the discussion: maybe a flywheel being spun up by a falling weight, then addition of the concept that potential energy is "0 at infinity" for gravitational fields etc and a problem about escape velocity from Earth.

Now your notes would look something like this:

ENERGY: Energy is always conserved. <example of an energy diagram in 2d>. Applications: if we can quantify the energy something starts with and how that energy changes, then we can calculate other useful quantities about it: example: a ball starts 10m up at rest, then we can determine how fast it is moving when it has fallen 10m. <Example problems 1,2,3 from the lecture, with short notes on the side as to what is being introduced each time>

Pretty simple. Maybe 1-2 pages. But a 40 page reading is a huge amount of extraneous information compared to this lecture. It will probably feature a narrative style describing (1/2)

>>8772920
>>8772958
What we are doing in a non-mathematical sense, why we are led here from previous topics, 8 pages of history and famous experiments, a page talking about energy conservation and some irrelevant nuances to it, a whole page devoted to one ball example that reiterates a ton of previous material and how it applies to the ball, then multiple more pages for the remaining examples including detailed sidenotes about the mathematical techniques used, and then 5 pages of conclusion including an appendix and a "review" section.

The trap is thinking everything in the reading matters. As a general rule, write down major definitions and theorems, and while you can read every corollary and subdefinition and example, you have no interest in them beyond having been exposed to them once.

Tl;dr try not to take readings too seriously because it is easier to learn by doing problems after being exposed to the material quickly than to read everything and try to understand it all. In addition, do readings parts at a time interspersed with the relevant pset sections.

Most of all, uncertainty and inadequacy is a part of learning. As a kid this is anxiety, later it becomes frustration or blase (high school), and as a continuing student, it will hopefully turn into "comfort in uncertainty": learn to recognize that stumbling sensation as the process of developing skill and aptitude within your own mind. You're still stuck in the anxiety phase, so your task is to push yourself to acquire comfort in uncertainty. Accept that you don't understand, then methodically go back.

Understanding and internalizing this was a turning point in my college career, intellectual development, and entire life. It's something most people will never achieve, because it is a long process and requires discipline and self reflection. But everyone who is professionally successful in physics or math has absolutely acquired this comfort.

>>8772975
Thanks, anon, this has been super helpful.

>>8772975
the books have been rewritten over 50 times, of course every paragraph has substinnce, evne the dumb 'this is why cuz of its history' passages

File: IMG_20170323_212228723.jpg (1MB, 2432x2256px) Image search: [Google]

1MB, 2432x2256px

>>8771955
>>8772025
>>8772117

File: 16602620_1282289888472909_1680852537278208721_n.jpg (59KB, 564x564px) Image search: [Google]

59KB, 564x564px

>Be me.
>Going to CC. Parents don't pay for the college. They allow me to live in their house though.
>When and/how/should I go about getting loans to pay for my education?
>What kind of job can I get where I can make shit money, but get paid to study?
Currently work 16hrs/week doing foodservice. It sucks, but so do my time management skills.

>>8772975
Not that guy, but thanks. You're a baller, anon.

>>8773011
I might have come off like I was saying they have no substance or value. That's not what I meant. What I mean is that there is a difference between the "close reading" that you do to a dense textbook vs. the "reading" you do to lower-stakes material.

Try to read Rudin like a novel and you won't learn anything. Try to read a novel like Rudin and you'll die of boredom.

That's the analogy- we aren't literally talking about a novel, but there is just no reason to stress over close-reading history like you would close-read a theorem. In fact the mistake of close-reading texts like this is what causes so many premed-types to be enormously inefficient when studying: they think carefully highlighting pages of pure text will help them, when all they should be doing is trying to understand the example

>>8773011
>>8773033
Further, I would add that books are almost always written as a *resource*, not a chronological introduction to the material--in short, they aren't even necessarily MEANT to be read straight through. They have all those detailed examples, notes on mathematical techniques, motivation paragraphs, etc, so that when you diagnose what you don't understand, you can go reference that specific part.

When you hear the phrase "read pages 72-105", you implicitly add "in order" and think you have to read them straight through like an essay. But instead of "read pages 72-105 in order" what is really being expected is "be comfortable with the relevant material from page 72 to 105".

>>8767837
Take all the statistics courses you can.

>>8773028
You could do some biking delivery. Doing sports sure helps learning.

If you have to learn while working, find a job where no one will interrupt you (like watching cc-tv but I'm not sure that shit exists).

File: Capture.png (12KB, 670x50px) Image search: [Google]

12KB, 670x50px

how do i find this?

>>8772069
Please help. I can calculate the initial flow rate based on the delta p and delta a, but then the pressure will decrease proportionally to volume of liquid, and I don't know how to express/plot it

>>8773278
nevermind i figured it out

File: asfd.png (18KB, 660x66px) Image search: [Google]

18KB, 660x66px

can someone tell me how to work this? i know the answer is 50sqrt(2) but i cant figure out how to get to it. i'm getting 100sqrt(2)

>>8773584
[eqn]y=100t,x=0 \\
D = \sqrt{(y-0)^2+(x-90)^2} \\
D=\sqrt{10000t^2+8100} \\
\frac{dD}{dt}=\frac{10000t}{\sqrt{10000t^2+8100}} \\
100t=90,t=\frac{9}{10} \\
\frac{10000*.9}{\sqrt{10000*.9^2+8100}}=\frac{9000}{90\sqrt{2}}=\frac{100}{\sqrt{2}}=50\sqrt{2}[/eqn]