/sqt/ - Stupid Question Thread

Could someone check a couple of simple Linear Algebra problems?
Thanks

And another one

>Given valium right before surgery
>High all day (at least noticeable when lying down)
>Take a bar of Xanax I had lying around (8x my prescribed dose for insomnia) before a flight to be comfy
>Nothing except some short term amnesia
I'm legitimately curious, why?

How is a and b any different from each other? Does that mean momentum is conserved in the x direction and i only need to calculate for the y direction?

well, they give you the speed and direction after impact. so the momentum changes in both the x and the y direction

still confused?

I don't think there's such a thing as uncountable infinity, or at least that the reals are not uncountable.

You can count them by listing all numbers representable in x digits, moving on to x+1 once you've listed all of them in x, like so:

x = 1: -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

x = 2: -99, -98, -97... -10, -9.9, -9.8, -9.7...

Where is the flaw in my argument? Or should I get the Nobel Prize in mathematics?

>Where is the flaw in my argument?
that there's no rigour in it

Can you be more specific?

Doesn't my method count every real?

it doesnt even count all the rationals, 1/3 would never be counted

I don't know what's more retarded. The fact that you think the reals are countable or the fact that you think there's a Nobel Prize for Mathematics

What if I add the caveat that you count all fractions and roots with x digits?

pls no bully

Could you please provide me me a most simple and graphic example of a feed forward loop?

You'd still be missing uncountably infinite transcendentials

How do I find the length of a function graph at a segment? Like if you took the line, laid it flat, and measured it.

en.wikipedia.org/wiki/Arc_length#Finding_arc_lengths_by_integrating

[math] \int_a^b \sqrt{(f'(x))^2+1}dx [/math]

Gotcha, thanks for being civil.

Chances that i get into Umich for EE PhD with only 2 summer of research experience? Both are EE related research, but only one is related to my chosen specialization (electromagnetics)

I am a laymans.

If there is more CO2 in the atmosphere due to climate change won't that mean we cannot use carbon dating anymore as the carbon will get into the fossils?

Is there a way to date things without carbons?

Assume 3.95 gpa, 166/160/5 (Q,V,W) gre

you'll never get the Nobel prize in math with that attitude

Is there anything special about the point where f(x) = integral [0, x] (f(x))? I realize e has this property but I'm wondering about other functions. I also feel like an increasing function should generally have exactly 1 such point but don't know how to show that,

pic related
why isn't a cone's lateral area equal to the lateral area of a cylinder that has bases of circumference equal to the circumference of the cone at the midpoint of the slant?

If I do this, I'm getting the formula H * pi * R where H = cone height, R = cone radius
instead of the actual formula, which is S * pi * R, where S = slant length of original cone.

i mean, the way I saw it was that I could take away the bottom excess part and stick it to the top half and make the whole thing a cylinder that has a circumference equal to the one of the cone at its midpoint

oh right, if you try to stick it to the top you'd have to squish it, and squishing it implies that there will be some "excess" material

the quantity of the excess material increases as the difference between the slant length and height increases.

I'm guessing this has to do with the fact that we're dealing with volumes here, not with linear values, since I'm trying to morph the shape and stick it to the top and make the whole thing cylindrical

is it a smart choice to do a PhD in harmonic analysis with focus in financial signal processing? what is the job outlook? will I be able to make good money?

Is there a way to take math classes at a university I'm not enrolled in? I'm done with ODE and no CC's offer courses higher than it.

what's the difference of 'taking' a class and 'enrolling' in a class?

What I meant to ask is if there's a way to take classes at a university I'm not seeking to get a degree from. Like 1-2 classes a semester type thing.

Hi ! i'm trying to code using LaTex but there's something bugging me :
Each time i write the = symbol, it looks like a - since one of the two bars is nearly invisible.
Is there a package or something like that to make the = symbols more visible ?

Yeah you should be able to. You could always just email the university too

No. But if the class is big enough you can just show up.

Does anyone have any cryptology books they would recommend? I'm a wee undergrad with only one abstract algebra course, so a book with a primer would be useful.

I'm trying to create some encryption software, but the most I've created is the polyalphabetic cipher.

Cryptonerd here. I highly recommend running through this:

cryptopals.com/

Most cryptosystems fail not because someone doesn't understand the maths behind , but because of problems you learn about in those challenges.

Ya, so I'm guessing you haven't actually printed it out. The way the pdfs make typically means that computers without crazy resolution make it look like a minus sign.

You could solve this a couple ways (or you could simply realize that it isn't an issue):

you can make your ='s all bold ( \textbf{ } ) or you could use a different font for your documents. That isn't too hard, so you can just google that.

I ran into this problem for a bit, but then realized that if you zoom in to read or just simply print off your notes when you want to study from them, it's a non-issue.

I will do that this weekend! Thanks, user.

Hey guys, I'm really torn on what to pursue between electrical engineering and physics. I am going into my third year of uni and my first two years have been in EE. I have been doing a physics minor as well so have all the lower level classes needed for physics major as well. To be honest I would be happy studying either subject and so just want to know what would be best in terms of job prospects etc.. I want to pursue a MS or PhD with whichever I choose and probably work in a lab outside academia afterwards. With all of this in mind, which would y'all choose and why?

i would choose electrical just because its more interesting to me and i beieve it have more job prospects.
i think i would need a major in physics to get into research or high tier jobs and im not great at math so less plausible

If relativity is right, what's the point of going faster in time if you're actually going slower in time by going faster? I mean, if you cross a galaxy in the speed of light, it will seem as if the galaxy aged waaaay more than just the time it would take to run across the total distance at the speed of light. In other words, if you're late to work and you speed up your car, you'll be even later to work if you actually went slower instead of faster. Einstein sure is stupid.

is [math] \mathcal{M}_{m,n}(\mathbb{N}) [/math] a standard notation to denote the set of m by n matrices with natural number entries?
ive seen something similar for real and complex numbers, but idk if thats just because theyre fields. not sure why that would change anything though.

Where do you guys go to look when trying to find textbooks?

any advice for an algorithm that picks the drum beat out of a song?

I've been thinking that since it's so easy for a human to do that a computer should definitely be able to do it.

I'm not stupid- I will not be trying the latest neural network python library. I will probably do a trial and error system that tunes the BPM (which is usually around 80-150) to find some kind of envelope.

Just wondering if anybody has tried anything similar and knows something I don't about doing this type of shit

quick whats a nice wiki to read about science while I try to sleep

Experimenting it.
Take some cyanide and see how your body "reacts"...

go do look more like or something fgt

How much work do you usually have to do in a bullshit requirement class like philosophy?

Lets look at the 2D and the 3D case:

Take two line segments from the triangle, one above the midpoint and one below. They will have length 2*(r+a*x) and 2*(r-a*x) where r is the radius in the middle, a is the slope of the triangle and x is the distance of the two segments towards the middle
adding the lengths of those two segments will give you 4*r
simply taking the length of the middle segment twice will give you 4*r too.
Thats why it works in 2D

Now for the 3D case

Take two circular segments, each with the the distance x to the middle.
They will have the respective areas pi(r+a*x)^2 and pi(r-a*x)^2 where r is the radius of the middle segment and a is the slope of the cone.
adding those two up will give you 2*pi*(r^2+(ax)^2)
which is strictly bigger then taking twice the middle segment 2*pi*r^2
Thats why the method won't work in 3D anymore

I hope that makes sense outside of my head

Never seen that notation, but I'm pretty sure it means what you think it means.
A common notation is [math] GL_n(F) [/math] in a group theoretic setting which are the invertible n x n matrices over a field F.
The notations [math] F^{n,m} [/math] or [math] F^{n\times m} [/math] are pretty common aswell

Is A and A or B the same as A and B?

If you mean A and (A or B), yes
If you mean (A and A) or B, no

oops i fucked up, sorry.
it's not even true in the A and (A or B) case

Libgen

>If the terms of an infinite series don't approach zero, the series must diverge.

Is the inverse of this statement true? If I take the limit of an infinite series and it approaches zero does it necessarily converge?

no, consider a_n= 1/n

no : 1/n

fuck my shit up. I'm in ODE and I've never done anything related to series and my final has over 50% series on it.

What test would I use for 3/n^3 and (-1)^n(3/n^3)?

how did you make it this far

I went to a school that did Calc 1 (Differential) Calc 2 (Integrals) Calc 3 (Series and Sequences) and had Multivariable as it's own separate class. I took all of the above except Calc 3 there.

Since I took multivariable I was eligible to take classes like Linear Algebra and ODE at my new school despite never learning about series.

Ratio test and alternating series tests, respectively

Thanks senpai. I see why the second one would use the alternating series because of the (-1)^n, why would you use the ratio test for the first?

Is the amount of matter infinite within an expanding universe?

1. Given a ring of matter (such that the attraction is disbursed over 1/m^2) would not a ring or torus of matter circulate around it?

2. Wouldn't the fact that it's more likely for particles to be amassed within the ring pull the ring internally closer?

3. Wouldn't the ring constrict and alter the shape of the torus?

Question: Could such a structure exist in the universe?

btw, this image would be a cross-section of a torus where the ring is contained within the open area of the torus circularly.

is there an objective test to determine if someone is transgender?

what's more likely to happen first, extraterrestrials visit earth or earthlings detect extraterrestrial life?

This depends upon either how easy it is to detect their travel before their travel finds their way to us.

tl;dr;
Detection is more likely than visitation

>get bullied at job
>hahaha how is it real just quit your job

Stupid questions don't exist. but inquisitive idiots sure do.

no, it's a feelings thing

I'm of the opposite opinion
stupid questions exist but stupid people do not

so why is the 'treatment' genital mutilation instead of therapy?

Assuming you mean [eqn]\sum _{n=1}^{\infty}\frac{3}{n^3}[/eqn], that's a constant multiple of the convergent series [eqn]\sum _{n=1}^{\infty}\frac{1}{n^3}[/eqn], so it also converges. Your alternating series converges absolutely because the corresponding series of absolute values of the terms converges. Alternating series test only shows conditional convergence, which is a weaker condition. I'm only a calc 2 brainlet so please forgive me Veeky Forums if i'm wrong.

Oh and don't forget that you can also do the root test [math]\lim_{x\to\infty}\sqrt[n]{\left|a_n\right|} = \rho[/math]
Which converges for [math]\rho < 1[/math], diverges for [math]\rho > 1[/math], and inconclusive for [math]\rho = 1[/math]. Pick up a calc 2 textbook and go over the various tests for convergence. That person who said to do the ratio test must have read it as 3/3^n, since that would be easy to do the ratio test on. I believe the ratio test is inconclusive for the series you gave.

fuck, i meant [eqn]\lim_{n\to\infty}[/eqn]

WOMEN ARE THE OPPRESSORS! EVERY YEAR WOMEN WORLDWIDE KILL 50-60 MILLION OF THEIR OWN BABIES BY WAY OF ABORTION, WOMEN ARE EXTERMINATING THE FUTURE OF MANKIND(BOTH FEMALE AND MALE FETUSES OF ALL RACES)! FEMINISM IS MENTAL ILLNESS, IT'S DESTROYING ALL PEOPLE!

I concur.

I'm stuck on this question. How do I calculate the angular velocity of crank AOD?
The bearing B moves at a constant velocity of 0.9m/s. I don't know how to find the velocity of the crank from that

I just had an exam question where I had to find the critical points of the trace function (the usual function from R^(n^2) to R). I had no idea in the exam and I've still no idea now. So, does anybody know how you'd go about it?

does it have any critical points? even just looking at n=2

x1 x2 -> x1 + x4
x3 x4

partials [1, 0, 0, 1] which always has rank 1, in higher dimensions you always get n ones and n^2-n zeros

the trace is a linear map so its differential is the map itself. and because the trace is obviously a non-zero linear map, it has no critical points.

It's not standard but it makes sense

Actual answer is boxed in the bottom, Everything else is solid until the final step of the integral isolation, i have no idea why it's 1/34. Can anyone shed some light?

disgusting handwriting

can't read any of this garbage but you should just have to do integration by parts twice to get the original integral on both sides and other known known terms on one side, then you just solve for the original integral

If I have a Hamiltonian
[math]H = \frac{1}{2m}(p_{i}-eA_{i}(x))(p_{i}-eA_{i}(x))[/math]

How do I do the Legendre transformation to get the Lagrangian?

stop bullying, his handwritings fine

so why can't you spot the mistake?

you didn't keep track of any of your equal signs brainlet

the last equality you wrote doesn't follow from anything

I can, the mistake is using the trig functions as the integrating factor, do the integration by parts the other way round

wrong brainlet
see
since adding 9/25*(integral he wants) to each side you get the coefficient 1+9/25 = 34/25, this gives the desired answer