/sqt/ Stupid Questions Thread

how do I find a function given its fourier series?

What came before the big bang?

>>7769617
intuitively:
the wavelength of a light wave is the distance between the "peaks" of the wave, right?

If study a beam of light that comes from the left towards the right with a wavelength [math]\lambda[/math], and you move to the right with speed [math]v>0[/math], do you agree to say that you will meet more peaks than me? (since you are catching up to them).

Notice that if light moves at the speed of light, it doesn't mean that the peaks themselves move or move at the speed of light.

>>7770058

if you have a vector and a basis, you can find the coordinates of that vector on that basis by projection.

Now replace "vector" by "smooth periodic function", "basis" by "every possible exp(i*k*w*t)", and "coordinates" by "fourier coefficients"


The fourier coefficients are just the coordinates of a periodic function on a basis of complex exponentials.

>>7769617

Same as for sound.
If you move towards it, frequency will go up, if you move away, frequency will go down.

>>7769617
The practical answer is given already,but the interesting point is that by compressing the wave peaks you actually increase the energy. And this happens even tho it may be the observer who accelerates towards the light source.

>>7770069
wait sorry if you move to the right you meet less peaks

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Britbong here, what do?

>>7769617
What in the world is going on in that picture? Is that some sort of weird fraternity ritual?

>You must successfully gut and stuff these chickens
>Then play Counter Strike for 12 hours

Also I hope those lads washed their hands before using the computers, otherwise they're going to give someone salmonella.

>>7769617
What is that weird phenomenon in science where when a person looks in a microscope and observes a certain object it's placement depends on who the observer is and where they expect it to be.

And what is the explanation of whatever that is?

>>7769617
If time exists, and there's permanence to out actions does that mean somewhere in someplace I am always existing like my 12 year old self decades ago is somewhere in some realm doing what I was doing decades ago. And does the existence of time imply that we are all in some sense immortal because we're always existing in that point in time?

>>7770063
Matt Damon.

>>7770098
You're in AS maths, get out of here underage.

I : The consciousness that my brain creates.

Free will : The I can independently from its external forces make decisions. If you were to travel back in time its absolutely possible that the I will choice differently this time.

I will call this the classical viewpoint on the subject, because I feel most people define these terms in this or very similar ways.

Now to my question: How can free will be true if external forces affect your brain and ultimately your consciousness. How can the premise of "choosing differently" be true, if the universe is deterministic. Even if it turns out that the universe is indeterministic, how can you prove that the I has any control over your body, if your brain and hence the I is controlled by external forces? (Biology, Hormones, etc)

How does the journal submission process work? If my paper was just assigned an editor, roughly where am I at?

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How do you apply a shear transform in the x direction to a generic real function y = f(x) ?

I already know how to apply a shear transform in the y direction to a generic real function -- to do that, you simply take the function y = f(x) and change it to:

y = f(x) + kx

for some constant k.

But what do you do to apply a shear transform in the x direction to f(x)?

I've tried the following, but my graphing calculator shows that it doesn't work:

y = f(x + kf(x))

What am I doing wrong here?

Pic unrelated.

>>7770302

You can't do it with a real function.

The problem is that when you shear a real function horizontally, it might cease to be a real function, because the shear might cause it to fail the vertical-line test.

For example, imagine y=x2 sheared horizontally by 45 degrees. For some vertical line, it will intersect two points on the sheared parabola, which disqualifies it from being a real function.

To solve this, switch over to the parametric equation (x,y) = (t, t2). Now you can shear it horizontally by changing it to (x,y) = (t + kt2, t2).

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Listen up faggots, is this correct?

T-t-thanks.

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I asked this before, but I can't find it in the archive where I did and the thread 404'd fug.

Anyways, I'm transferring from aerospace to mechanical engineering, since I believe if I just play my cards right, I can do whatever I can do in aerospace with mechanical. (And if i still don't feel like I can, I'll think about grad school)

Mechanical engineering doesn't require physics III and lets you take Computer Data Structures as a sub. Now, aerospace didn't require physics III either, so maybe this question is a moot point...

Am I missing out on anything for my major by not taking physics III? Only thing I can think of would be relativity perhaps, but I wonder if I would really learn enough in it to really constitute a miss by not taking the course.

Should I just stick with Computer Data Structures? Let's me just go ahead and pursue a CS minor

Good laptops for academic work? I'm starting grad school in the fall (math) and have been using the same shitty Gateway running Ubuntu for 5 years now. It's falling apart and runs like shit, and I've decided to replace it.

I'm thinking about grabbing a Mac. Any input? I just want something that will run smoothly and last.

>>7770302
What part of physics is this? Is it Newtonian mechanics?? Because I just finished that course and am familiar with the concept but not familiar with this math

Why is the hotel management meme so hilarious

>>7770444

it is

>>7770489

>wants to do work
>buys a mac

cant tell if trolling or legit dumb question

get a dell or lenovo

>>7770522
I want to use Unix and I'm growing tired of mediocre Linux hardware support (e.g. my desktop can't use wifi).

>>7770520

Thanks senpai

I have a math competition coming up (up to cal 3, diff. Equations) I need help conducting speed mathematics in the calculus level, such as the tabular method for integrating by parts, what's a good source for learning these?

>>7770098
nigga you know the grad is 2, so differentiate the quadratic function and equate it to 2, then work out x, sub back into orig quad to work out y, the sub into first equation to find c you mong

So I applied to multiple colleges and have decided not to carry on with one of the colleges. Do I have to contact them and tell them or do I just not go through with the supplemental requirement, etc?

>>7770444
mathway.com

>>7770533
no the nigga that responded to you, but I think it's sad that you're the only one to even remotely aknowledge other people's response to your problem.
It's appreciated (from me at least)

>>7770499
What part of physics is this? Is it Newtonian mechanics?

No, it's just pre-calc. It;s learning how to do function transformations like translation, scale, reflection, etc. to better understand how the graph of a function works.

See:

https://en.wikipedia.org/wiki/Transformation_%28function%29

for the basic idea.

I think they teach it because it's good practice for calculus, to get the students used to the idea of doing function transformations -- because calculus rests entirely on two important function transformations: the derivative and the integral. As preparation for that, you want students to be already used to the idea of converting one function to another.

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>>7770063

Me

Into your mom.

How can a determine the salinity of a water sample (that only contains NaCl and water) with just a multimeter?

Why is i the square root of -1 and not the square root of -15?

is 0 an imaginary, a real, or a complex number? Because it seems to lie on both number lines - is it both?

>>7770698
Why would it be the sqrt of -15? i is a term so that we can solve problems easier, and 1 is the easiest number to work with.

>>7770698
First off, they defined i to be the square root of -1 because that's convenient, and easier to use. Also 0 is an integer, which is a subset of the rationals which is a subset of the reals which is a subset of the complex numbers.

>>7770698
>Why is i the square root of -1 and not the square root of -15?
Because it doesn't make a difference. If you used [math]\sqrt{-15}[/math], then you could just scale things by [math]\frac{1}{\sqrt{15}}[/math] to get back to the usual complex numbers. The theory of field extensions is relevant to this (and interesting).

>is 0 an imaginary, a real, or a complex number? Because it seems to lie on both number lines - is it both?
Every real number is a complex number. By definition, the set of complex numbers is [math]\{a+bi\mid a,b\in\mathbb R[/math]. Of course 0 is a real number, because it is included in the normal arithmetic of real numbers with which you are familiar.

>>7770698
>is 0 an imaginary, a real, or a complex number?

It's all of them.

Consider the following 3 numbers: 0, 0i, and 0+0i

All three are identical in the complex number system.

Because all three have an imaginary part of 0, they are also all real numbers too, and they are all identical in the real number system.

Because all three have a real part of 0, they are also all imaginary numbers too, and they are all identical imaginary numbers.

>try to see the scholarships
>they want references
>don't have any

Fucking normies.

>>7770098
First derivative of x^2 +6x +7 is 2x +6

But off the top of my head for part B, I think you use Newton's method.

>>7770489
Alienware

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>>7770098

Excuse me if i'm wrong, it's 2am and i'm on sleep medication

>>7770489
The new Dell xps 13 is a good bet

>>7770225
30%

Getting pretty fucking frustrated with this - this is basic shit I'm sure but I can't find anything about how to do this.

Trying to find k.

[math]2x^{2} + 2kx + k = 0 [/math]

Any ideas?

>>7770937
k=-2x^2/(2x+1)

>>7770098
Pretty easy senpai

Just differentiate the second equation, you'll end up with an equation in the form [math]2x+c[/math]

As for the second part, just set your [math]2x+c[/math] equation equal to your other equation and solve for x.

>>7770944
How did you get to that?

>>7770944
think you missed the k in 2kx

>>7770946
The derivative of a function is the slope of the tangent to that function in a specific point man, not the tangent itself...

>>7770937
Are we assuming that k is a constant number? Because >>7770944
basically just rewrote the equation in terms of k, which isn't wrong per say.

>>7770961
No it isn't. f'(x) is the gradient at any given x.

Differentiate the curve on the right to get the gradient at any given x.

Eqn on right: y=2x, gradient is 2

so f'(x) = 2

Solve for x

Put that into f(x), solve for y

Now go back to y=2x and see how you need to translate it to make y of 2x + c equal y of [math]x^{2}[/math]+ 6x + 7

You now have your c

>>7770960
No he didnt

>>7770964
Yeah, k is constant

>>7770960
Not me, this is me >>7770946

How did you get to that?

>>7770136
kek gabe

my apologies for asking this, as even though it is a stupid questions thread, it is way out of context as to what is currently being posted.. but i am fucking shit at math, like basic math tier, can't do much else than basic multiplication and everything else below (addition and subtraction) how fucked am i? i still haven't taken the act or sat even though i've graduated and im having a sort of "mid life crisis" because i realized i probably will be fucked if i do not go to school. wat do?

>>7771110

go to community college and go to remedial Math. Start studying 6 hours a day at least. If you still don't get it, study for 12 hours. Only take Math if you have to.

>>7771119
do i not need act/sat scores for community college? once again sorry for really stupid questions, i really never considered much after highschool during.

>>7771126

No. Anyone can go to a CC. Just apply to your local one. Well, if you're from America anyway. I'm not sure what the CC equivalent is in other countries. Just google your nearest community college and there should be steps on how to apply to their CC. If still confused then just post your city and I'll help you find a CC.

>>7771130
im about to move in a few months, and im currently working to do so. do you think it's better idea for me to just study now for free until i move and then start going to school once i move?

>>7770692
Rekt

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Is a third impact possible?
Happy late third impact day btw

>>7771131

Well, if you're gonna move somewhere far, then sure just wait. Spring semester has already started for most people, so I doubt you'd get into a class anyway since they might be filled up. You can probably check the schedule at your local community college and see. Go to khan academy or youtube for the lecture and try pirate a book to do some of the problems.

When I was doing Math I used this guy. https://www.youtube.com/user/patrickJMT

Pirate here:
gen.lib.rus.ec/

MIT OCW on youtube may also have low level lectures. I'm not sure.

What city are you going to move?

>>7771148
Thank you for all the info and help in general. Very much appreciated. I'm heading to Philadelphia around may/june. I'm gonna be living with two friends who will be/are in school so hopefully that motivates me further.

>>7771152

Well, here's a CC in Philly.

http://www.ccp.edu/

There you can apply and after you apply you're gonna have to go to the school and take an assessment test which decides where they want to place you in English and Math. It's good to try to get a handle of basic Math now so that you don't have to take multiple pre-requisites. I'm not sure what your major is, but if it's Engineering then the higher you get placed then the less Math you will need to take.

When you do go to college make sure you get the good professors here:
http://www.ratemyprofessors.com/

https://oasis.ccp.edu:4051/pls/prod/bwwsksear.PW_SEARCH
https://oasis.ccp.edu:4051/pls/prod/bwwsksear.PW_FOUND_BASIC

If I were you, I'd get a good foundation by starting all over with basic arithmetic and work your way up to Elementary Algebra.

Here's some notes, btw.
http://tutorial.math.lamar.edu/


Good luck.

>>7771187
thank you so much. yeah, i want to major in something which will provide me with good earnings (obviously) but as well remain interesting. so something stem, all i really needed was to reup my math skills. but i very much appreciate the actual help.

>>7770764
It's not a pure imaginary. It's only real and complex.

>>7770080
that's not how special relativity explains it

I am trying to understand this:A straight line has an angle of 180 degrees.A bisector is a perpendicular line dividing that angle into 2 right angles.An angle has only 1 bisector and through a single point can pas only one perpendicular line.Now I have this simple question:How can there pass through a straight line more than a single perpendicular line if each perpendicular line is a bisector to a 180 angle and there can be only 1 bisector.Sorry for asking such a retarded question pls try not to be too harsh.

>>7771504
>How can there pass through a straight line more than a single perpendicular line if each perpendicular line is a bisector to a 180 angle
It's a different angular sector for each perpendicular line (the vertex is not the same)

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hey /sci/ is this legit algebra? i had a factor of root x with v_A, but the question asked for the fraction on the bottom left. i ended up doing this weird algebraic maneuver which i don't really trust but it gets the right answer. can someone tell me if i've done something stupid but fluked the correct result or if this is actually legit?

>>7771524
wtf

>>7771524
[eqn]\frac{1\times 2-5}{3}=\frac{1-5}{3}[/eqn]
Seems legit

>>7770630
>

I used that, but it gave me a different answer.

>>7771524
you're not showing any work so it's hard to tell what the fuck you even did but it doesn't seem correct

the only way to get rid of the factor of sqrt(x) is to divide by it and you clearly didn't do that because you didn't divide the v2 term or the (x+1) term

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Why the fuck do they want me to take the GRE in order to apply to Grad School? The GRE is largely math based and nothing on that damn test has anything to do with what I got my degree in and my grades should be sufficient evidence of my performance.

why the fuck do they want me to take a 6 hour math test when I'm not a fucking math major?

Also is there a way to get around taking the GRE and still go to grad school? I fucking hate math and don't want to be studying up on that bullshit to apply to a program that has jack shit to do with math in the first place.

>>7771532
that is literally all my working - just cancelling the sqrt(x) like that. it's dumb as fuck but gets the right answer which is confusing me.

if i divide everything by sqrt(x) then there would be a sqrt(x)^-1 on the v_2 of the numerator, but the question asked for the result as a pure fraction with no factors.

>>7771532
>you're not showing any work
Oh I'm so fucking glad I don't ever have to hear that shit anymore. Who the fuck cares how I got the damned answer so long as it is the right answer.

>show your work
>show your work

Bitch I do some of that shit in my head.

>>7771540
If you can do it in your head, fine. I don't give a shit.

If you want help because you don't even know if your answer is correct, don't post a few equations and expect me to reverse-engineer what you did and THEN review it for you.

>>7771539
well if you have to do a wrong algebraic manipulation you've obviously started the problem wrong you retard

>>7771543
wait you actually think >>7771540 is me?

i'm >>7771539 obviously

>>7771546
fair enough, don't think i did though :^)

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Hello /sci/
Can you help me with this baby tier problem?
What's the overall resistance between a and b?

>>7771608

By symmetry, the middle resistor is a virtual short/open circuit so the total resistance is 1Ω.

Generally:
https://en.wikipedia.org/wiki/Y-%CE%94_transform
You get a ⅓Ω splitting into two ⅓Ω+1Ω parallel paths which reduces to one ⅔Ω resistor. So the total is ⅓Ω+⅔Ω=1Ω∎

Hey lads, I am doing a mock-exam about general chemistry with a copied old exam.

There's this question:
Draw the Nitrate-Ion NO3^{-} and the Ehanolmolecule CH3CHO spatially correctly.
what do they actually want?

Sorry, not a native speaker.

>>7771626
Thanks for help anon.

>>7771515
Thanks for clarifying

>>7771634
They want you to draw diagrams of those molecules that give the atoms their correct locations in space. (i.e. reasonably correct bond angles, and possibly correct relative bond lengths.)

For instance, if they wanted you to draw methane, you'd draw a carbon atom with hydrogens attached in a tetrahedral arrangement.

At least, I can't think what else "spatially correct" could mean.

>>7771689
Agreeing with this guy.

>>7770865
Really? This is going more quickly than I anticipated.

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posted this in the last thread, dunno if it got a reply

can:
f(x) cts on [a,b]
f(a) = f(b)

be replaced by:
f(x) cts on (a,b)
lim f(x) as x-> a+ = lim f(x) as x-> b-

?

>>7770058

How do you find a function given its Taylor series?

>>7770457

Take Physics III, you learn way more than a Data Structure class and it's not that much harder.

>CS minor

No employer or grad school cares and it's a subject that's really easy to learn on your own.

>>7771762
I guess it's true but not much of a generalization. If you have the later you can always continuously extend your function f to [a,b] in a unique way and then use Rolle's theorem on that extendet function. But since a function with that property is basically continuous on [a,b] you dont really get to much new information.

>>7771689
>>7771692
so, in the VSEPR way?
Just make a VESPR drawing?

>>7771792
cheers

was thinking about stuff like tan^-2 and just wanted a sanity check

This is a pot smoking question.

Theres a big debate between smoking weed with hemp wick(a wax coated piece of hemp string) or smoking weed with a bic lighter.
People claim that using a hemp wick makes you more high and makes the weed taste better. Cannabinoids vaporize at a certain temperature, and hempwick burns at a lower temperature than a lighter. Hempwick users say that if you burn the weed too hot, you waste the cannabinoids and you get less high.

My question is if that you can "waste" the cannabinoids by burning them too hot? Or if its possible to "over-burn" any substance and destroy certain molecules.

The weed community is VERY un-scientific, and I don't want to perpetuate the stoner logic.

Learning to do substitution integrals, but there's one step in a particular case I don't quite understand:

[math]

\int \frac{x}{x^2+1} \\

\updownarrow \\

f(g(x)) * g'(x) \\

g(x) = x^2+1 and g'(x) = 2x \\

\int \frac{x}{x^2+1} * 2x dx \\

\frac{1}{2} \int \frac{2x}{x^2+1} dx
[/math]

I don't understand how we get 2x on the numerator. Shouldn't we get 2x^2 as we already have an x there so x * 2*x = 2*x^2 ?

Any input is welcome.

>>7771902
Also, here is the video that caused me the concern: https : //youtu.be/QmsWRiPZEjg?t=1m12s (I started at 1:12 since thats when he starts talking)
It doesn not sound like he knows what he's talking about, but I'm not claiming to know any better. If he's right, please tell me so.

>>7770965
Are you retarded?

>>7771232
> It's not a pure imaginary. It's only real and complex.

Incorrect.

0 is pure imaginary.

The definition of pure imaginary is a complex number with a real part of 0. The complex number 0+0i obviously fits that requirement. By definition, the complex number 0+0i is the same number as 0, so therefore 0 is pure imaginary.

>>7771909
No. You don't just add in a factor of 2x. You basically make the integral into that form by factoring out constants.

>>7771909
(Sorry I don't know how to make pretty math.)

Given:

y = INT x / (x^2 + 1) * dx

Define u = x^2 + 1:

y = INT x / u * dx

Note that du/dx = 2x; therefore dx = (1/(2x)) * du:

y = INT x / u * (1 / (2x)) * du

Move the constant factor out of the integral:

y = (1/2) INT x / u * (1/x) * du

Simplify:

y = (1/2) INT 1 / u * du

Solve the integral:

y = (1/2) ln |u|

Substitute u = x^2 + 1:

y = (1/2) ln |x^2 + 1|

>>7771928
Tell me how that's wrong.

Is this a legal move?

[math]\sqrt{3}-4sin\O cos\O =

\sqrt{3}-2sin^{2}\O
[/math]

>>7772004
wew my latex broke

\O = theta

>>7771960
For future reference, you need to use the word "math" in brackets to begin using latex and "/math" to end. You just have to learn commands at that point, which are fairly straightforward.

>>7772008
>>7772004
same guy

[math]\sqrt{3}-4sinA cosA =

\sqrt{3}-2sin2A
[/math]

corrected the latex

>>7772034
why wouldnt it be? you're using an identity

>>7770520

No... it isn't.

Here's my stupid geometry related question.

Let's consider some *object* (curvature, Lie bracket, whatever), which can be equivalently expressed as a mapping from a product of some copies of tangent and cotangent bundle (defined only on smooth sections) to the space of smooth functions. Suppose that this mapping is C^infinity - linear in every component. Does this imply that said object is a tensor?

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>>7770520

You got him good.

>>7772334
Not quite sure what you mean by 'tensor' (are you filthy physicist scum or something?), but you should look inro the Serre-Swan theorem (Swan's part), and something called 'the main theorem of differential geometry' or something like that in chapter 0 or 1 of Besse's book on Einstein manifolds.

>>7772344
Serves him right for posting a sideways picture.

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>>7770063
>What came before the big bang?

This guy obviously

>>7769617
Why doen't current flow through the core of a transformer? Explain for DC and AC.

Question:

If i want to build a robot at home (say something like you see in battlebots or robot wars), what programming language(s) if any would be required?

ALSO

If i wanted to build an automated robot, one which i do not control but pre program to do tasks, which language(s) would I need to use?

>>7772555
you mean current from the wires?
Because they're insulated

if you mean eddy currents, there are some, but you can counter it by using laminated magnets.

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How does he get (12.5)?
I've tried myself:
[eqn]\frac{\mathrm{d}\mathbf{X}}{\mathrm{d}\tau} \cdot \frac{\mathrm{d}\mathbf{X}}{\mathrm{d}\tau} = c^2 \mathrm{d}\tau^2 = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right) ^2 (c^2 - \mathbf{v}\cdot \mathbf{v}) \\
\mathrm{d}\tau^2 = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right) ^2 (1 - \frac{v^2}{c^2}) = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right)^2 \gamma^2 (v) \\
\frac{\mathrm{d}t}{\mathrm{d}\tau} = \frac{\mathrm{d}\tau}{\gamma (v)}
[/eqn]
And get that, not [math] \frac{\mathrm{d}t}{\mathrm{d}\tau} = \frac{1}{\gamma (v)} [/math] as derived here in the pic.

>>7772810
[eqn] \frac{\mathrm{d}\mathbf{X}}{\mathrm{d}\tau} \cdot \frac{\mathrm{d}\mathbf{X}}{\mathrm{d}\tau} = c^2 \mathrm{d}\tau^2 = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right) ^2 (c^2 - \mathbf{v}\cdot \mathbf{v}) \\
\mathrm{d}\tau^2 = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right) ^2 (1 - \frac{v^2}{c^2}) = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right)^2 \gamma^2 (v) \\
\frac{\mathrm{d}t}{\mathrm{d}\tau} = \frac{\mathrm{d}\tau}{\gamma (v)} [/eqn]
stupid 4chan, hopefully this works.

>>7772812
welp
[math] \frac{\mathrm{d}\mathbf{X}}{\mathrm{d}\tau} \cdot \frac{\mathrm{d}\mathbf{X}}{\mathrm{d}\tau} = c^2 \mathrm{d}\tau^2 = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right) ^2 (c^2 - \mathbf{v}\cdot \mathbf{v}) [/math]
[math] \mathrm{d}\tau^2 = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right) ^2 (1 - \frac{v^2}{c^2}) = \left( \frac{\mathrm{d}t}{\mathrm{d}\tau} \right)^2 \gamma^2 (v) [/math]
[math] \frac{\mathrm{d}t}{\mathrm{d}\tau} = \frac{\mathrm{d}\tau}{\gamma (v)} [/math]

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>>7772813
>>7772812
>>7772810

I'm so sorry to ask this again, I guess I did not get a response either because It's too stupid or I'm bothering.
See, I'm having the MEXT scholarship test. A scholarship that allows you to do a full undergrad in Japan fully paid (would go study to muricah or yurop but don't have money) and this is my only oportunity to study outside of my shitty third world country (Paraguay).
Can I get some advice on how to approach this?
These are the syllabi for the test. Plus japanese and english test + interview.
http://www.jasso.go.jp/eju/syllabus_math_e.html
http://www.jasso.go.jp/eju/syllabus_math_e.html
http://www.jasso.go.jp/eju/syllabus_math_e.html

>>7772810
12.5 is just a manipulation of the fact [math] d{\tau ^2} = - d{s^2} [/math].

>>7772831
Ah thanks, I've got it now.

I need to find points of discontinuity using the definition. The function:

f(x)=floor(x)*cos(0.5pi*x)

I'm guessing they are for all x=+-1,2,3... but I don't know how to prove it with the definition

>>7770063
The big bang was essentially the beginning of physics as we know it. Any questions involving time or space before the big bang hold no real meaning.

>>7773225
careful
of course floor(x) is discontinous at the points you mentionned.
But if cos(0.5*pi*x) is 0 at one of those points, it doesn't really matter does it?

In reality, the discontinuities of f are a subset of {0,+/-1,+/-2,...}.

Try to find which ones.

If I have a RL series circuit and I use direct current, after a long time the inductor will become like a short circuit, storing magnetic energy during the process. If I then remove the power source, this energy will be released and will generate a current which dies exponentially.

My question is, does this current flow in the same or in the opposite verse as the one that "charged" the inductor?

>>7772367
cunt

>>7773287
if the source has a voltage V, then the current from the positive side of the source to the negative side is V/R (1-exp(-R*t/L)), which starts at 0 and tends to V/R at infinity.
Now if you "remove" the power source, the current becomes V/R exp(-R*t/L), which is still positive, and tends to 0 at infinity.

So the current flows in the same direction.

When an object is moving relative to a reference point, how does the distance between the object and the point change? Does length contraction apply?

>>7773310
thanks anon

also the opposite happens in a RC circuit, right?

>>7773235
thank you based anon

Question concerning number sequences: Given the difference and the first term of an arithmetic sequence, how would I find the first term to exceed a certain number. For example: find the first term in the sequence to exceed 3000.

>>7771530
Are you 100% sure your answer is right or that you wrote it down correctly? I never had any real issues with mathway.

>>7773366
The n-th term of the sequence [math](u_n)[/math] with difference r is [math]u_0 + nr[/math].
Finally, all you have to do is solve the inequation [math]u_0 + nr \le 3000[/math]

f is a continuous non-negative function defined over [0,1].
f(1)=f(0)=0
Show that for every 0<r<1 exist 0<y,x<1 such that |x-y|=r and f(x)=f(y)

wut do

>>7773458
Doodle something, that's the no. 1 reflex to get

>>7772643
You mean the wires or the core? I thought the wires were just open copper. Is there coating or something on them?

>>7773497
I doodled but it's not helping much with the proof.
I'm trying to say f gets a maximum value there at point m, so exist m<x<1 and 0<y<=m such that f(y)=f(x). I'm just not sure how to make |x-y|=r for every 0<r<1 happen

>>7773502
hint:
for every 0<r<1, f-r crosses the x-axis at at least two points.
Let a(r) and b(r) be the leftmost and rightmost points, and d(r) = b(r)-a(r) (the distance between them).

What can you say about this function d? What is its minimum value? What is its maximum value? What theorem can you then use?

>>7773500
of course there is...
The wires have coating (varnish I think in English) to insulate them from each other (they're tightly wound) and from the core of course.
Otherwise the current would just go through the wires perpendicularily, it wouldn't follow the long path.

>>7773509
>f-r crosses the x-axis at at least two points.
why?
no idea about d(r) honestly...

>>7773520
Awesome, thanks. If you have practical knowledge on transformers please do share.

>>7773526
Sorry not f-r, but f-z for example, with 0<z<m

draw a function f

lower the graph a bit

it has to meet the x-axis at least twice :)

the distance between a(z) and b(z) is r(z)

you can show that r(z) takes all the values between 0 and 1 using the intermediate value theorem and the continuity of r(z)

>>7773531
what more do you wish to know anon? I'm not a fan of transformers but I used some :)

How do I get better at math proofs? Like there always seems to be an obscure manipulation trick you have to do to get from the given to the goal

>>7769617
Can real and complex numbers fit along the same one dimensional line or can we only interpret them as a 2D plane?

>>7771145
Third Impact never happened because that lazy hack Anno never released 4.0

>>7773537
thanks for bearing with me... I think I can carry on from here, but I'm not sure how to explain r(z) is even continuous

>>7773502
Okay, now that you have doodled, let's think about how to reword the question.
What you want to prove is that there are x, y such that |x-y| = r and f(x)=f(y), right ?
Can you see why it is equivalent to finding an x such that f(x+r) = f(x) ?
Now, you have reduced the number of reals you want to find and the problem is reduced to finding a zero to the function x-> f(x+r)-f(x).
Now, consider the function g(x) = f(x+r)-f(x) and see what you can do with that.

>>7773421
Thanks, man. Just another quick question: can the equation [math]u_n=u_1+(n-1)d[\math] be written as [math]u_n=u_1+u_0[\math]?

>>7773602
Well unless d = 0 no, for the obvious reason that [math]n \to u_1 + (n-1)d[/math] is not constant whereas [math]u_1 + u_0[/math] is

>>7773613
Oh sorry, I meant (how the fuck does latex work on sci?) can [eqn]u_n=u_1+(n-1)d[\eqn] be written as [eqn]dn+u_0[\eqn]?

Hey, i'm kind of stuck here trying to get the value of a series:
[math]\sum_{n=1}^\infty \frac{1-k}{k!}[/math]
I kind of figured i would need to use the exponential series to solve it, but on the top part of the fraction there would have to be ^k to use it.
Also i don't think an indexshift is the solution here but i'd be gladly proven wrong.
[math]=> (1-k) * \sum_{n=1}^\infty \frac{1}{k!}[/math]
Help would be greatly appreciated.

>>7773633
https://sites.google.com/site/scienceandmathguide/

with [@math@]@latexStuff@[@/math@]
and without the @

>>7773633
Oh, in that case, yes of course (since [math]u_1 = u_0 + d[/math])
To use inline latex write your code between [ math] and [ /math] tags

>>7773645
[math] \frac{test}{test} [\math]

>>7773655
you have to use this one / on the math tag.

>>7773640
Use the identity
[math]\frac{1-k}{k!}=\frac{1}{k!}-\frac{1}{(k-1)!}[/math]

>>7773658
Oh, I'm severely autistic, thank you.
[math]\frac{\sqrt{test}}{test}[/math]

>>7773640
Split the sum:
[eqn]\sum_{k=1}^{\infty} \frac{1-k}{k!} = \sum_{k=1}^\infty \frac{1}{k!} - \sum_{k=1}^\infty \frac{k}{k!} = \sum_{k=1}^\infty \frac{1}{k!} - \sum_{k=1}^\infty \frac{1}{(k-1)!} = \sum_{k=1}^\infty \frac{1}{k!} - \sum_{k=0}^\infty \frac{1}{k!} = -1[/eqn]

>>7773661
Huh, in the preview I got the right result [math]\frac{\sqrt{last}}{test}[/math]

>>7773655
>>7773661
I always try it out in here https://hack.chat/?xqvonbha on a random channel before posting.
you can try it on there with $ tags, for example $ latex $.

>>7773660
Alright thanks anon!
>>7773663
That makes sense thanks a lot.

>>7773580
uhhh show that g gets one positive value and one negative value so it's 0 somewhere? Otherwise I have no idea

>>7773663
Thats true but you have to be carefull you are only allowed to do that when both parts converge absolutely (which they do in this case). Another way to proof this without splitting the sum would be by using the fact that this series is a telescoping series.

>>7773580
g(0) = f(r)-f(0) = f(r) >0

g(1-r) = f(1) - f(1-r) = -f(1-r) <0

>>7773671
Yup, now aren't there two obvious points to consider ?

>>7773686
So it would work like that:
the series is a telescope series therefore the limit which the sequence of the series converges to is also the value of the series?
for
[math]\sum^\infty_{k=1} \frac{1-k}{k!}[/math]
the sequence would basically be
[math]\frac{1-k}{k!}[/math]

Is that correct?

>>7773550
>there always seems to be an obscure manipulation trick you have to do to get from the given to the goal
I'd say that this is rarely the case. It sounds like you're just proving identities, so you can start with what you want to show and then try "working backwards."

>>7773695
I can't see any... x isn't 1 or 0

>>7773706
Not quite. A telescoping sum is a sum where all the terms except the first and the last one cancel each other out, so you are left with the first term, beeing a fixed number and the last one which is still dependent on the n of the n-th partial sum. Then you can just take the limit over this terms. In this particular case it would like this:
[math]\sum_{k=1}^\infty \frac{1-k}{k!} = \lim_{n\rightarrow\infty}\sum_{k=1}^n \frac{1-k}{k!}=\lim_{n\rightarrow\infty}-\sum_{k=1}^n \frac{1}{(k-1)!}-\frac{1}{k!}=\lim_{n\rightarrow\infty}1-\frac{1}{n!}=-1[/math]

>>7773750
Damn whats wrong with my Latex? It looks fine in the preview.

Is there a quick way to expand (x-a)(x-b)(x-c) etc. ?

File: Screenshot_11.jpg (20KB, 488x282px) Image search: [Google]

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>>7773750
Okay i get it now, thank you.
Not sure why it won't display though.

>>7773753
Same for me, I don't get it.

>>7773758

That is to say, is there a fast way of expanding
[math]\prod_{n=1}^k (x-x_k)[/math]
My apologies, I'm not used to using Latex

>>7773758
Actually, yeah.
https://en.wikipedia.org/wiki/Elementary_symmetric_polynomial
Plug the roots into these bad boys. For reference, this can be found in the Galois theory chapter of Artin's Algebra.

>>7773776

That's perfect and a little simpler than I thought it'd be. Thanks anon.

>>7773776
Thats pretty neat.

If z is a complex number with Re(z^n)>=0, for all n in N, prove that z is a nonnegative real number? How do I do this? Thanks

>>7773839
If z is a negative real number, you're done. So assume that z has nonzero imaginary part and show that [math]\operatorname{Re}(z^n)<0[/math] for some n.

Can someone give me the intuition behind integration over a boundary? I am doing independent study on complex analysis and I understand how everything unfolds but I never could quite visualize what it really means to integrate on a boundary. This is particularly troublesome when reviewing Green's Theorem.

>>7770098
fuck math lol

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>>7773874
Well in the picture you see a visualization of the integral across a curve. You can think of the boundary as a closed curve.

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>>7773892
I think it clicked, so basically with pic related if you have a function p(x,y) we are basically summing up (integrating ) all of those areas to get the equivalent volume on the RHS. Thanks a lot bro.

what comes behind the university
i mean scientists say the universe expands but
if it expands it must go somewhere

>>7773911
http://io9.gizmodo.com/5799335/five-weird-theories-of-what-lies-outside-the-universe
You might want to read this if you talk about what comes after the observable universe.

I personally imagine it as a space were we wouldn't ever be able to explore its limits, if it even has them. When they say the universe (observable) expands i think of that space being filled up or colliding.

>>7773907
I dont know this particular version of Green´s Theorem but basically yes. The interesting thing about this and some similar results like for example cauchy's integral formula or most important stoke's theorem is that you can say something about the integral of a function or even the function itself over some domain just by looking at function on the boundary of said domain.

ANTIBIOTICS
from what i know antibiotics are made from mold
now bacterias are geting resistant but could it be posible that other planets have new mold species and new antibiotics

I'm a pleb trying to get some better intuition for Euler's formula, but I can't understand what sort of magic this is:
[eqn]\DeclareMathOperator{\cis}{cis}
\sum_{n=0}^{\infty}\frac{i^n}{n!}={{\cis}}(1)[/eqn]

There has to be an explanation for this. What's the relationship between exponential growth and the radian that allows it to be defined this way? It's killing me.

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>>7774130

>>7774130
>What's the relationship between exponential growth and the radian that allows it to be defined this way?
look at the maclaurin series expansions for sin, cos and exp

Find all real numbers a in [-2,2] so that the following is a recursive sequence : [math]x_0=a [/math] and [math]x_{n+1}=x^2_n-2 [/math] for all n in N so that [math]x_{2016}=a[/math] This is supposed to be solved with trig, but I am not sure how?

How do I review calculus up until differential equations in 2 months, step by step?

>>7770831
That's it.

Should I do an "A level" math exam where I have to get 65% right to make my points equivalent to the 90% of "O level" or should i just make an o level. (I'm not in and English school btw).

>>7774286
O level:
http://dload.oktatas.educatio.hu/erettsegi/feladatok_2015tavasz_kozep/k_matang_15maj_fl.pdf
A level:
http://dload.oktatas.educatio.hu/erettsegi/feladatok_2015tavasz_emelt/e_matang_15maj_fl.pdf

You didn't specify, but I assume you mean first order diff eqns. I don't know how recently you last studied math, so the list is pretty long. The content is straight out of my first college text book. I skipped some of the less useful stuff, and included some things that will help you get back into the mindset of doing calculus. You can start wherever you feel comfortable:

1. Functions {algebraic (polynomials) and transcendental (exponential, trig)}

2. Limits and derivatives {definitions of limits, continuity, derivatives & rates of change, differentiability, rules of differentiation, implicit differentiation, differentials, l'Hopital's rule}

3. Integration{Anti derivatives, Reimann sums (not really necessary, but can be helpful in understanding the nature of integration), Area Functions, FTOC}

4. Applications & Rules of Integration{Substitution, Areas between function, Volumes and Surface Areas of revolution, Integration by parts, trigonometric integrals, trigonometric substitutions, integration of rational functions by partial fractions, Improper Integrals}

That should be a pretty good review. If you are also doing higher order diff eqns, I would strongly advise going over infinite sequences and series + Taylor series & Maclaurin expansions. Honestly, I doubt any course would start straight off the bat doing diff. eqns, so you will probably review what you need before starting.

>>7774247
Sorry, forgot to add post number. >>7774325

>>7769617
WTF is going on in the OP pick.

can i prove something with induction like this :
after showing S works for S(n=1) show induction via S(n+2) rather than S(n+1)?

>>7774371

Well if you prove S_1, S_2 and then S_n+2 that should be enough

>>7774371
yes, why not, but it's always easier just with +-1

>>7774239
this anyone?

>>7774377
>>7774378
thanky

>>7774331
thanks

>>7771780
Yeah, I think that's what I'm gonna do unless somebody talks me into thinking that I really won't use anything in physics III in mechanical engineering.

If anybody wants to chime in, I would appreciate opinions.
Otherwise, cheers anons

>>7770098
I never understood how anons here can go on and on about shit like manifolds and topology like it's nothing but then act this way towards high school math

>>7775385
Just so we're on the same page, /sci/ is in fact more than one person.

>>7775385
I never understood why anons here worship topology as if it was the hardest

>>7770063
the big erection

>>7770937
Lets imagine that we have two functions, f(x) = 2x^2 + 2kx + k (the function you presented), and some unknown function, g(x), that graphs the position of the trough as k changes. This means that the trough from f(x)'s parabola will always be touching the line computed by g(x). So knowing this, we can say that when f'(x) = 0, then f(x) = g(x) for all values of k.

Looking at the derivative of your function we can find:
f'(x) = 4x + 2k
Let f'(x) = 0,
k = -2x
x = -k/2

This stays true for all values of k if k is a constant.

From here you can find the function for g(x) in terms of both x and k and make more sense of it. If you would like I could also go through that.

>>7770944
This is actually wrong, the proper value for k is -(4x^2 - 2x)/(2x + 1), which can be simplified further:
k = -(4x^2 - 2x)/(2x + 1)
= -2x(2x + 1)/(2x + 1) = -2x

>>7771524
Just so it's easier to write, Va = a, V2 = b.
a*sqrt(x)/b - 1 = sqrt(2x/(x+1)) - 1
x(a^2/b^2) = 2x/(x+1)
a^2/b^2 = 2/(x+1)
2b^2/a^2 = x+1
x = 2b^2/a^2 - 1

Subbing x back in we get:
(b*sqrt(2) - b)/b = sqrt(2x/(x+1)) - 1
sqrt(2) - 1 = sqrt(2x/(x+1))
1 = 2x/(x+1)
x + 2 = 2x
x = 2

Without more info a and b cannot be resolved as values because the nature of the equation being diophantine.

Regarding your question about this being legit algebra, the answer is yes and no.

We can see that b^2/a^2 = 3/2, which is true for what you have written. You have a correct solution, however what you did is still incorrect. We cannot define a solution with finite values because there is not enough information (due to this being a linear diophantine equation). Try to think more about what you can prove definitely rather than finding a fitting solution.

>>7770112
Are you trying to get at Heisenberg's Uncertainty Principle?

>>7770937
[math]
2x^2+2kx+k=0
[/math]
Factorise for k
[math]
2x^2+k(2x+1) = 0
[/math]
Shift the [math]2x^2[/math] to the other side and divide through by the [math]2x+1[/math]
[math]
k=\frac{-2x^2}{2x+1}
[/math]

How many distinct three letter anagrams can be found in SLEEPLESSNESS (doesn't have to be real words)

how to design function for all n letter anagrams
how about any N letter starting word

>>7775707
This is only true for when the solution is k = 0.

>>7775713
64260.

If you need explanation it might be a little bit difficult and long for me to write it out in a way that would be easy to understand. Basically you can find out what the combinations are progressively, adding a new layer (new unique letter) at a time. The function for each layer is defined as f = (q+1)[q(k-1)+1] - C, where C = Sigma(i) * (k-1) for i = 1 to i = q. k is the number of elements in the newly added letter and q is the number of unique elements not including the one from the current layer. Multiply all the values of f you have calculated together and you get the answer.

>>7773911
>what comes behind the university
Depends. If you're a physics major, it's McDonalds.

>>7769617
I have a really important question

So suppose I'm thermodynamically analysing a process and I'm calculating the generated entropy (or whatever you call it in English) using the equation in my pic. Does T stand for the temperature of the system or the surroundings giving it heat or taking heat away from it? For a reversible process that doesn't matter, but I'm not sure which one to pick for an irreversible process ...

I'm self-studying, so I can't ask my professor or something

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>>7776095
Forgot my pic

>>7776096
>>7776095
temperature of the heat source/sink

in general, the equality is only valid in case of a reversible process though
If it's irreversible, it's most often an inequality

>>7773230
says you cunt

I'm struggling with mass spectrometry. My professor told me to use the Skoog and to study there, but frankly I didn't understand well enough the sources (EI, MALDI, etc.). What book would you guys suggest?

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>>7769617
Are electrons just very high frequency light?
Can oscillation of an electromagnetic field be zeroed and disappear?
Is this notion of a granular "photon" just how a given measurement device will detect and view a high enough amplitude in an underlying field, or can a granular discrete unit actually be said to exist?

Do quantities even exist, or are they dependent on a given scale and measurement device? I find it hard to believe spacetime is actually continuous. The universe acts like it's quantized in all ways.

>>7776125
I'm actually wondering about the case when it's an inequality. I also find it weird because Wikipedia says it should be the system.

>>7776137
no, it says (or should say) the temperature at the interface.
Which is forced by the external temperature since temperature is continuous.

>>7776133
>Are electrons just very high frequency light?

No. light = [math] e^ + + e^ - [/math] pair

>>7776263
I don't understand. Are you saying light decays into a positron and an electron? So light is actually more "macro" than an electron itself?

>>7776267

Very high energy photons can decay that way

Can you calculate a one sided derivative by simply finding the derivative function and then applying a one sided limit for the given point?

>>7776288
Consider a function defined by x^2 for negative x and x for positive x. What is the derivative at 0 that you are trying to use?

>>7776290
In your case I mean taking the derivative of x^2 and the find the limit of it as it approaches 0 from the left.
My function is defined as f(x) = 0 for x = -1/2 and f(x) = exp(-(x/(1+2x))) otherwise. I need to find the derivative at -1/2 from the left side. Can I just differentiate the exp shit and find the limit of that as it approaches -1/2?
The derivative surely exists, as it's defined at -1/2 and it's continuous from the left, but I'm not sure how to say this rigorously.

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>>7771145
Yes, but in the form it happened in serial experiments lain.

http://www.ratemyprofessors.com/ShowRatings.jsp?tid=248526

Should I even bother or take someone else at a different community college?

Let [math]\mathcal{F}[/math] be a collection of disjoint open subsets of [math]\mathbb{R}[/math]. Prove that [math]\mathcal{F}[/math] is countable.

Someone helps me please.

>>7776413
Maybe Borel-Lebesgue theorem could be helpful.

>>7772413
sauce of your YHWY pic?

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>>7769617
So I'm looking to up my note taking game a bit better this year and write cleaner notes, so I was thinking of taking them in graph paper rather than lined so I am a bit freer to organize things without adhering to the grid and have it look funny like with lined paper?

Is this a good idea? If so, should I go 4 x 4 or 5 x 5, and does anybody have a suggestion on where/what brand to buy? Or are they all just naturally a little expensive?

>>7776413
you can find a rational number in every element of F

Hi /sci/, it's /tv/ here. Sorry to ask you a stupid question, but it's been bugging me for months now.

How dense is Godzilla exactly? At his smallest and lowest weight, he's 50 meters tall at 20,000 tons, and at his heaviest/ largest, 90,000 tons and 110 Meters, so what's his density in cm/3?

I know it's pointless seeing as it's a fictional creature, but it's been driving me nearly insane for a while now.

>>7774063
>Antibiotics are made from mold
No, penicillin was discovered on a mold and is produced by certain molds but not all antibiotics are made from mold most are made through enzyme reactions with penecillin (or some other antibiotic) as a substrate.

Bacteria are getting resistant to penecillin based antibiotics because they are so widespread, thus the need to alter penecillins structure to keep it functioning. There are certain antibiotics specifically used for drug resistant diseases, there is also research being done into antibiotics that do not target cell membranes and instead inhibit the bacterias awareness of similar specied cells nearby which prevents them from becoming virulent or trying to inhibit excretion/reproduction in bacteria.

This is an area of massive research and huge success without needing your pop-sci "space has the answer" solutions.

>>7773765
>>7773753
\frac {} {} not \frac{}{}
Here's what he wrote:
[math]\sum_ { k=1 } ^\infty \frac { 1-k } { k! } = \lim_ { n\rightarrow\infty } \sum_ { k=1 } ^n \frac { 1-k } { k! } =\lim_ { n\rightarrow\infty } -\sum_ { k=1 } ^n \frac { 1 } { (k-1)! } -\frac { 1 } { k! } =\lim_ { n\rightarrow\infty } 1-\frac { 1 } { n! } =-1[/math]

>>7775553
underated post

>>7776466
http://www.amazon.com/MUJI-Notebook-A5-size-Unruled-80sheets/dp/B00MFB7NDE/ref=sr_1_6?ie=UTF8&qid=1452547822&sr=8-6&keywords=plain+paper+notebook

>>7776480
assuming godzilla has roughly the same proportions as a human

if he's 50 meters tall, he must have a volume of around 25500m^3

which means his density is around 0.8

if he's 110meters tall, he must have a volume of 270,000m^3, which means a density of around 0.3

>>7776614
Damn, really? That's a lot less dense than I thought.

>>7770107
>>7774360
anon said a guy donated a bunch of chickens to a youth center (i don't remember if the chicken were dead or alive or if it was unspecified)

>>7776680
I think they fucked up on his weight, you can tell the person who decided it had no idea what they were doing

Every night for the past year or so, separated by a month between, I get extremely itchy. It has gotten to the point now that I lay in my bed just thinking about the itchy spots, and now they half small raised bumps. It is present during the day, but it unnoticeable if I am not paying attention.

WebMD and stuff says allergic reaction, but I don't know what could be causing it. I don't have any food often enough that it might be doing it to me I believe, but I am not sure. Allergic reaction also doesn't sound quite right because all I have is skin reactions and I need to itch, itch, itch but I can't get the feeling to go away. The bumps are that bad tonight, but I have been forcing myself not to scratch. Any ideas what it could be/preventative measures?

>>7777609
Probably folliculitis. Rub some alcohol on it.

>>7777623
The bumps are skin colored and all the ones I see on Google are red and infected looking (seeing as how that is what folliculitis is). Is it normal for it to just be a patch of maybe 15-30 bumps in one spot that are skin colored?

>>7775866
lol actually its 80

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>>7777930
cont

every three letter word is in one of three categories:

1, composed of one letter
2. composed of two letters
3. composed of three letters

in each category
1. only 2 possibilities: eee and sss
3. every letter is different, there are 5 letters to choose from (S L E P N) so there are 5P3 = 60 in this category

2, where there are 2 different letters in the word, one of them (S L or E) appears twice

ie for S repeated, you get three permutations for each other letter which is 12, and so 36 in total

2+60+36 = 98

okay so its 98

>>7777967
That is wrong. You can write a small program to write out the permutations and you will get well over 98.

>>7777979
go on then

the key is DISTINCT permutations.

so pee and pee (with the e's the other way round) counts as one, not two permutations

otherwise the answer would just be 13P3
which itself is only 1716

This is a 3 parter.

How feasible is it to mine asteroids for resources?
How close are we to mining asteroids for resources?
How would the potential influx of new resources affect the world and economy?

>>7777609
I have had the same problem last winter for weeks, it was awful. I remember I have even failed a midterm because I had spent too much time scratching.
I think a doctor I visited said it was because I have dry skin and because it was very cold outside. Not sure if it's right though.
What I did was first vacuum everywhere in my room and wash everything (in case it had been allergy), then switch from soap to a hypoallergenic thing and then use a skin cream (for the dryness).

>>7777609

Sounds like eczema my dude

I feel so fucking stupid.
How the fuck does a-(-b)= a + b?
Same with (-a) • (-b) = ab

>>7778142
first realize there is no such thing as "-"

- only stands for an operation with the inverse of an element.

if the inverse of b for the operation + is denoted by "-b", then you can show -(-b) = b

so in reality, a + (-(-b)) = a + b

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>>7778142
A negative times a negative is a positive

>>7778142
for the second one, you are looking for y = (-a)*(-b) right?

let's find y + (-a)*b first.

y+(-a)*b = (-a)*(-b) + (-a)*b = (-a)*(-b + b) = 0

so y + (-a)*b + a*b = a*b

since a*b+ (a-)*b = 0, you are left with y = a*b

>>7778142
Visualize a line where the centre has point 0. To the left you will have the negative integers in ascending order and the same with the right and positive integers. If you want to run the operation a-b you would go to point a and move b spaces to the left. If you wanted a-(-b) then you would go to point a, but instead of moving to the left (for subtraction), you would flip the orientation (because you are subtracting a negative number, meaning you flip the orientation because you are subtracting a negative number).

Another way to think about it is that there is an imaginary +1 or -1 at the start of every symbol (to denote if the value is positive or negative). So we could write the equation as (+1a) + (-1)(-1b). Because we are multiplying -1 and -1b we get a positive b.

>>7778162
>>7778167
You guys are based, thanks

How to self-study math from books effectively?

I have hypoglycemia, but I've never heard any plausible explanation as to why it exists. Does anyone know? Does my body just suck at producing glucose?

>>7769617
>Every finite set is compact.

Let [math] A [/math] be a finite set and let [math] \{ O_ { \lambda } | \lambda \in \Lambda \ } [/math] be an open cover for [math] A [/math]. Since [math] A [/math] is finite then it is always be possible to find an open finite subcover [math] A \subseteq \bigcup_{ i = 1 } ^{ n } [/math]. Thus A is compact.

I think I should justify the part where I say that you can always find a finite subcover for A, but that seems to pass for intuitive and obvious that if O covers A then you can find some finite sub-collection that still contains A.

>>7774239
bumping for this, thanks

>>7778474
Just pick for each point a in A an open set [math]O_a \in O[/math] that contains a. Then [math](O_a)_{a\in A}[/math] is a finite subcover of O.

>>7778582
Write [math]x_n = 2\cos(\theta_n)[/math].
Then, for all n [math]x_{n+1} = 4\cos^2(\theta_n) -2 = 2\cos(2\theta_n)[/math] so [math]x_n = 2\cos(2^n\theta_0)[/math]
Now to conclude, there are some calculations to make I think.
You can notice that if [math]2^2016 \theta_0 = \pm \theta_0 \mod 2\pi[/math], then [math]\theta_0\in \pi\mathbb Q[/math] so I guess you can do some arithmetic there, I'm still thinking about it

>>7778637
Thanks, but I am not sure how to go on, and why do you have [math]2^2016\theta_0[/math] ?

>>7778654
bro...

take the formula for x_n and plug in n=2016

that guy did all the work for you

>>7778200
>read exposition
>follow proofs in great detail
>do exercises
>revisit sections you realize you don't fully understand

>>7770098
X is equal to both function. Y in the first equation is equal to the -1/a from the second

>>7770444
No prob there fag

>>7770698
0 isnt a number is just a convention to separate negative number from positives

>>7778678
Have you read the actual problem? It's not that easy.

>have 4.0 GPA
>no awards
>no honors
>no experience
>no projects

Is this the surest way to get fucked in life?

>>7778953
No.
>have 2.0 GPA
>no awards
>no honors
>no experience
>no projects

Stop trying villainize good grades.

So ya stupid lay-man here.

If you have two very large (enough to have time observable time dilating effects by themselves) masses, but the measuring device (you or a clock or whatever) is in between them so that the gravitational forces are cancelled out completely, will there still be relativistic effects or will those be cancelled out too?

I had been contacted by a professor to work on a project. I am a sophomore. I know shit in how to program component and barely know what is a OP-Amp. Is he expecting me to know all this stuff, or he is waiting until I learn more about the subject from my classes.

>>7770098
>underageb&.

>>7774239
Define [math]f(x) = x^2 - 2[/math] then the problem reduces to finding all solutions for
[math]a = f^{2016}(a) [/math] with [math] a \in [-2,2] [/math].
[math]f^n [/math] is the n-times composition of [math] f [/math] with itself.

The equation [math]a = f^{2016}(a) [/math] is a polynomial equation of degree [math] 2^{2016} [/math] so it has at most [math] 2^{2016} [/math] solutions and it's very easy to find them all.

The solutions are
[math] a = 2 \cos \left( \frac{ 2 \pi k}{2^{2016} - 1} \right) [/math] with [math]k = 0, 1, \ldots, 2^{2015} -1 [/math]
and
[math] a = 2 \cos \left( \frac{ 2 \pi k}{2^{2016} + 1} \right) [/math] with [math]k = 1, 2, \ldots, 2^{2015} [/math]

Which can easily be checked by plugging them in the equation. Those are [math] 2^{2016} [/math] different solutions so they are all of them.

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Pardon me, but I'm trying to teach myself statistics. I'm only a beginner and there's something that has me stumped.

So I have an independent event that has a 1% chance of happening. For example, rolling a 1 in a 100 sided die. In a perfect world, if I attempt the event 100 times it would happen at least once. However that's obviously not true. The event event could still never happen or happen more than once.

So how would I calculate approximately how many attempts I should try to get a specfic result? ie; how many times I would have to roll the die before I get a 1? Or is it impossible to accurately calculate after all?

>>7779430
probability is 1/100. sample space is (countably) infinite.

>>7779239
Thank you, I hope that would suffice.

For the chemfags out there, any good easily available solvents that would dissolve and remove DDT and other petrochemical compounds, but not terribly damage (mostly) cotton cloth?

>>7779509
So then, the chance of getting a 1 if I roll two dice are the same if I roll two dice? Or five or ten? The number of trials doesn't matter at all?

I mean, the odds in one attempt are 1/100 right? And if I was trying to get two 1's in a row, that would be 1/100 x 1/100 = 1/1000.

Except I'm not trying for multiple results. Just rolling until I get one 1. Shouldn't I eventually get a one if the number of attempts goes to infinity?

>>7779581
You can calculate the odds of not rolling a 1 after n trials and then make that as small as you like by increasing n.

>>7771799
yes. Dreidimensionale form. Form spatiale de la molécule. So some atoms poking out and stuff.

>>7771768
Try to make your way to the series given known taylor series as the basis

>>7779581
The probability of not rolling a 1 is 0.99^n, which you can use to determine the probability of rolling a 1. So, for example, there is a 36.6% chance of not rolling a 1 if you roll 100 times. Increase that number as much as you wish to get the odds you want, but remember to keep in mind the gambler's fallacy when you're doing calculations such as this. Each time you roll the die there is still a 99% chance of not getting a one, so it is theoretically possible for you to never roll a 1, unless you have infinite trials.

>>7770112
There's not.

The closest thing is confirmation bias, but that's the equivalent of catholics seeing the virgin Mary in burnt toast rather than physics voodoo.

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>>7778142
Just made a post to find someone already asked this kek

Every video and tutorial tells me HOW to do it, Mathsisfun, Khan Acadamy, YT videos
But it still doesnt make sense! How does a number like number -8 jump all the way from the negative side and into the positive?

No explanation so far works for me, I'm about ready to accept genuine retardedness

>>7779904
You're being sarcastic, right?

>>7779928
Nope. I can remember to always treat subtracting negatives like postiives etc.. I can pass this easy.
I just wish I could understand what I was doing.

>>7779904
Think of why a double negative is a positive. E.G. OP is never not a faggot.

Also, negative is just a label denoting the absence of something.

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>>7779944
>Think of why a double negative is a positive. E.G. OP is never not a faggot.
..It cancels out?

4-(-8) somehow equals 12.. the two minuses turn into a plus? I can't see how this works in relation to number, although I understood your double negative sentence analogy..

>>7779944
you realize you're being trolled anon, right?

Is agriculture basically a branch of botany?

>>7779999
agriculture confirmed for sub-botany level

peasants just have meme jobs

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Why isnt the amazon more red on this map

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>>7779961
If you take away a positive number, you have less. Therefore, if you take away a negative number, you have more.


Think of it like vectors in a 2-D plane, but don't worry about anything on the Y-axis. See picture.

>>7780075
Ok so looking at the 3rd last line:
If I take away a negative, that's just a tedious way of saying, I'm giving you something?

Does that analogy work?

>I have 3 bananas..... and I see you should have 4, so I'm taking-away your missing banana problem and giving you another one

>>7778142
>>7779961
>>7780075

You can, if you think about it, apply the vector explanation to multiplication too. For multiplication in any dimension, you add the polar angles of the vectors and multiply the lengths of the lines.

For 1-D number lines, there's only two directions, positive and negative. A vector in the direction of the positives would have an angle of 0, and a vector going negative would have an angle of pi.

So when you multiply two positive numbers, you multiply their "lengths" or distance from 0, and add their polar angles (0 + 0 = 0).

When you multiply a positive by a negative, you multiply their lengths, and add the angles (0 + pi = pi). That's why a positive times a negative is negative.

For negative times negative, we multiply the lengths and add the angles (pi + pi = 2*pi). In polar coordinates, 2pi radians is equal to 360 degrees, so we've effectively gone back to an angle of 0. That's why two negatives multiplied together gives a positive number. Their "angles" add up to a multiple of 2PI, which is the same as 0 as far as angles are concerned.

You can do this without the radian notation if you want. The angles start with the positive line and swing counterclockwise around 0. PI = 180 degrees, 2PI = 360 degrees, which is the same as 0 degrees.

This might be a lot to take in if you haven't learned anything about vectors or are new to spacial math. Try drawing some of what I said out, and hopefully it will make some sense.

>>7780083
Sorry, should be "You have 3 bananas", but that's just semantics and I think you get the idea

>>7780075
We've all been taught that the minus symbol was the symbol for subtraction, but it could just as well be the symbol for anti-addition. So yes, that analogy works.

Writing 4 - (-3) is equivalent to writing 4 + (-1*-3)

>>7780089
>>7780090
The reason we are taught that way is because that's how math was first developed - counting. Somebody counting sheep wouldn't say, "We've added -8 sheep" if he lost 8 sheep. Similarly, he wouldn't say, "I lost -4 sheep" if he found 4 new sheep.

However, a different terminology had to be created when mathematicians started to develop algebra. Remember, many ancient civilizations had no concept of 0 or the negative numbers, so subtracting negatives would have been a mystery to them too.

>>7779930
Just think about it like this, anon. Subtracting is still adding. For example, 5 - 3 is just 5 + (-1 * 3), thus making 5 -(-3) equal to 5 + (-1 * -1 * 3), or 5 + 3

How much do other moons, planets or stars affect the gravitation on the surface?

Say, you're standing on the moon with the planet earth straight above your head and you launch something straight up. Compare that to being on the polar opposite side of the location you were just standing at and launch the same object with same amount of energy upwards. Is there a measureable difference?

Sorry.

>>7780273
Very little. There is a measurable difference though, since the effect of gravity is dependent on the distance from you to another object. The difference between the two is the same for any two points in space. Imagine the moon was gone. If you go to where one end of the moon would be, you feel X amount of gravity. If you go farther, to the other side, you feel Y. However, since the moon is so far away, and gravity scales on an inverse-square law, this difference is very small.

I have been drinking Lipton green tea for a while know but I recently read that low quality brands of tea contains fluoride and that Lipton is a shit brand.
Should I continue to drink it? Does the benefits outweigh the amount of fluoride?

>>7781526
There's fluoride in your water, dummy.