/sqt/ - Stupid Questions Thread

>how much linear algebra can i learn in 14 hours
>i have an exam tomorrow
how to drop out

I'm helping a friend design a user payout system (cryptocurrencies) for a sort of social network site and would like input for some questions posed.

youtu.be/FEZXDUy6YCU

y=mx+b b is y intercept m is slope start there buddy good luck :)

I hope you know what a matrix is

buy yourself a peanut tree

This bait is very tasty.

I need the immediate ancestor seeds. And like 200 or so genetically identical ones.
Peanut trees are real. It's a tree native to Australia that has a fruiting body with 8 to 10 edible black seeds that taste like peanuts

How do I show that the cross-ratio is invariant under projective transformations of the line [math]\mathbb{F}P^{1}[/math]?

yea, the movie?

Do you guys use solutions to study?
I often don't get how to solve a problem, then I look at the solutions and understand the strategy to solve it. The textbook have a lot of exercises so similar problems are common.
I feel anxious because the professor says we should try to solve the problems by ourselves.
There is no graded homework here.

Mathematica is the best CAS, period. But the Wolfram Language is rather... uncommon. You have to learn it to truly understand Mathematica capabilities.
If you want to get the work done without thinking about programming, try Maple. Is Java-based and a bit slow, but it works.

Repeating my question from last thread because nobody was able to help me:

How do I prove that that f(x, y) = x^2y + 1 is continuous in (0,0) using the epsilon delta proof?

I know that in order to prove this I need to prove that f(x,y) reaches its limit in (0,0) which is pretty clear from intuition, but I'm having a real problem proving it using the epsilon delta definition.

>How do I prove that that f(x, y) = x^2y + 1 is continuous in (0,0) using the epsilon delta proof?
>I know that in order to prove this I need to prove that f(x,y) reaches its limit in (0,0) which is pretty clear from intuition, but I'm having a real problem proving it using the epsilon delta definition.
What have you tried? It follows immediately by making use of easy lower bounds for |(x,y)-(0,0)|.

Good luck, we believe in you.

I think I got it actually.

|x^2y+1-1| = x^2|y| < ||(x,y)||^3 < 𝛿^3 = ε

So if you take ε>0 and 𝛿=ε^1/3 for x: 0

>I'm not sure what you mean by that. How would you write out the proof?
Essentially the same way you did (I meant the |x|

Is the angle for the slanted surface 90?
Also, how do i find the area of that surface when I’m given only 2 lenghths?

You are learning how to solve them, not the concept behind. If you managed to grasp the fundamentals you would not be having so much trouble. Personally i just think you are not studying right.

if you're in Australia, use
q + xw = λ

Any help with part b? The conclusion I'm supposed to verify is the statement on the bottom

Fuck your feelings. Stop feeling feels and start thinking logically, newfag.

>Any help with part b?
Use the hint.

If you're truly lost, look at a few lines at a time and try to do the rest on your own. Then go back a few days/week later and try to solve it again cold.

But try to solve it completely on your own for at least an hour before giving up. And speak to your professor for guidance in his office hours.

Probably

∮_γ dz = ∫ i*e^iθ dθ from 0 to 2π
z -> e^iθ

>Is the angle for the slanted surface 90?
nah it's 60, the angle is between the e vector and the vector perpendicular to the plane
>how do i find the area of that surface when I’m given only 2 lenghths?
you have a 60 30 triangle and are given a side, solve for the hypotenuse

I remember downloading a collection of all the books recommended on the Veeky Forums wiki a while back. Now my hard drive is dead and I lost them all. Anybody got a link or torrent for them?

Just download few books at a time and actually fucking read them.

Veeky Forums-science.wikia.com/wiki/Recommended_material

>Just download few books at a time and actually fucking read them.
Do you need to swear?

oh it was right there the whole time. I'm glad I posted my question in the right thread.
no

how do i figure out this problem? corresponding slide in next post

...

Thank you. It's not like I don't try to understand the concept (I try to demonstrate almost every equation by myself), but some questions are tricky.
I will try to not rely that much on solutions.

guys i need school advice.

I got in to u of Arizona for their optical science program and UIUC for their EE photonics track. These are both awedome schools that i didnt think id ever get in to. Where would you go?

Use Green's theorem and derive the Jacobian from the Hamiltonian.

Where do you live? I got into UIUC but didn't go because I live in California and I'm a greedy fucking Jew who prioritizes saving a few shekels over personal gratification. I regret it.

p-pls no memes

im just a brainlet user

> (You)
>Where do you live? I got into UIUC but didn't go because I live in California and I'm a greedy fucking Jew who prioritizes saving a few shekels over personal gratification. I regret it.

I live in Arizona phoenix area. So like 90 minutes from u of arizona

That's really not very far. Both seem equally appealing. How about this: If you feel more comfortable at home, go to UoA; if you're rich and don't mind travelling alone, go to UIUC.

what's a good linear algebra book

Gilbert Strang or whatever his name is for introducing LinAlg is okay plus you get his funny lectures

I know these are shallow as fuck but I still love having them around.

...

shit guys i really screwed up
i need to learn all of symplectic geometry by tomorrow and all i know is remedial college algebra
any good resources out there for quickly learning the intermediary material?

I'VE GOT TO LEARN ALL OF SYMPLETIC GEOEMTRY IN 1 HOUR 30 MINUTES.

What’s likely to be wrong with Sminem, medically?

Is there some genetic developmental disorder at play?

marfan syndrome

FOURIER TRANSFORMS

I know a shift in the time domain corresponds to a linear phase in the frequency domain....

But what does a shift in the frequency domain correspond to in the time domain?

He looks like an Elder Scrolls Oblivion NPC. Maybe he was downloaded and has no genes at all.

Let G be a group. If a topology on G is such that all left- and right-translations are homeomorphisms then it is called a homogenous topology. It is clear that a homogenous topology is determined by its system of neighborhoods at 1.

Does every system of neighborhoods at 1 determine a homogenous topology? You could just say that all left- and right-translations of all the things in the system of neighborhood of 1 are open but I'm having difficulty completing the proof. A 'paper' I was reading seems to use this without proof and there is probably something ridiculously simple I am missing.

How much (modern) algebra do you need to know in general as a mathematician?

anons pls this is urgent

hoffman&kunze

is there anything interesting that uses the golden ratio, which isnt a putting-golden-spirals-over-pictures-of-plants type thing?

Can someone explain how exactly we get 3l/4 and -5l/4 please? I can't really hazard a guess as to how those limits were retrieved and its kinda bugging me.

>How much (modern) algebra do you need to know in general as a mathematician?
None at all.

>mathematician as a job
bruh

either your field of study demands it or it doesn't, what the hell kid

>posts the solution, not the question
my guess is it's obvious from the question

Sorry, here's the question.

Should I be worried about Coronal Mass Ejections?

>total length is 2L
>midpoint is L
>midpoint +/- L/4

Hi did they get from a to b ?

How*

Sorry, I’m phoneposting.

need more context phonefag

Pic related seems to be the most obvious method in my eyes. But I am not sure what postulate/theorem they used for the initial transformation in the example i posted previously.

Sorry. This is two-valued Boolean algebra.

I can see how it is done algebraically to go from b to a and therefore to conclude that a is just (x+y) but I don't understand how to just directly infer the transition from a to b. Sorry m8.

Veeky Forums-science.wikia.com/wiki/Mathematics#Linear_Algebra

You should be able to guess it since the Fourier Transform is its own inverse.
en.wikipedia.org/wiki/Fourier_transform#Basic_properties

sin(18°) = 1/2φ
Fibonacci(n) = [φ^n - (-1/φ)^n]/√5 ≈ φ^n/√5
Since the worst case input of Euclid's gcd method are obviously the Fibonacci numbers, the max number of steps is n ≈ log_φ(√5*a).

2 years worth. One at the level of Artin/Herstein and another at the level of Lang/papa Hungerford.

Shitter schools that use lower books -> you're never getting tenure.

>Since the worst case input of Euclid's gcd method are obviously the Fibonacci numbers, the max number of steps
this is also (not coincidentally) related to the worst possible bound on approximation of irrational numbers by rationals, basically everything else is much better approximated (transcendentals especially so)

Because x=0 is set to where the axis meets the rod which is apparently l+l/4 = 5l/4 down it. as shown on the figure. The whole rod is 2l.

>x = x + 0 = x + xx'
>x = x + x
>x = xx
>x = x*1 = x(y+y')

x+x'y = x + x + 0 + x'y
= xy + xy' + x + xx' + x'y
= xy + x(y' + 1) + xx' + x'y
= xy + x + xx' + x'y
= xy + x + x'(x + y)
= xy + xx + x'(x + y)
= x(x+y) + x'(x + y)
= (x+y)(x+x') = (x+y)(1) = x + y

alternatively
>1 = 1 + y
>x = xx
>0 = xx'
x -> x*1 -> x(1+y) -> x(x+y)
x'y -> x'y + 0 -> x'x + x'y -> x'(x+y)
x+x'y = (x+x')(x+y) = x+y

2nd alternative
DeMorgan
x'(x+y') = x'y'
DeMorgan back
x+y

Could someone point to a resource where I can understand why for example taking a derivative of lnx=1/x, but of lny=1/y*y'? Also would like to understand taking a derivative of something with respect to something. I'm 100% those two concepts are connected, but my "teacher" never explained any. We just learned the rules. And I'd like to understand these through usage of Leibniz notation.

Also in pic related is the second one a second derivative and why is it written as such? I've only ever learned y', y", y"' etc. in school and this is new to me, but the teacher randomly started using d/dx, dt/dy/dx/dt and similar shit without even explaining the concept behind it. Fuck I hate my school.

>Could someone point to a resource where I can understand why for example taking a derivative of lnx=1/x, but of lny=1/y*y'?
That's just the chain rule (when y is y(x) and you're taking the derivative of lny with respect to x)

Okey, so I'm trying to show that Maxwell's equations (without sources of field) are not invariant by means of galilean transformations but invariant under Lorentz transformations. In the examples I've seen, they take some weird liberties on the chain rule, so I decided to try it defining everything properly. A time varying Electric field can be represented as a vector function [math]\vec{E}:\mathbb{R}^4\to\mathbb{R}^3[/math] and the same for a time varying magnetic field [math]\vec{B(t,x,y,z)}[/math]. So I just defined a composition of these fields with a galilean boost defined simply as [math](t,x-vt,y,z)[/math] and then applied the chain rule and found out all the partial derivatives are same except for [math]\frac{\partial\vec{E'}}{\partial{t}}=\frac{\partial\vec{E}}{\partial{t}}-v\frac{\partial\vec{E}}{\partial{x}}[/math]. With this extra term it was clear that the curl of the new [math]\mathbb{\vec{B'}}[/math] isn't the same as the one before the boost so I assume I was done. But then I did the exact same procedure for Lorentz transformations and I got a contradiction with Gauss's law as other terms appeared out of no where. Searching online I found out that People use also the Lorentz force and show how the fields transform under galileo/Lorentz, but I'm in a situation where I have no sources, so the Lorentz force shouldn't even come in this case.

I get that it's a chain rule, I just don't understand why there's a chain rule for lny but not for lnx. I guess I don't grasp the derivative of "1st" with respect to "2nd".

>I get that it's a chain rule, I just don't understand why there's a chain rule for lny but not for lnx.
x' = dx/dx = 1

Oh, Christ sorry I skimmed the thing. Thanks a ton for the help. Apologies for my thickness.

>Could someone point to a resource where I can understand why for example taking a derivative of lnx=1/x, but of lny=1/y*y'?
Only the second is correct.

However, by convention x is not a function of something else, so we can say that dx/dx is 1 and ignore it. If, for instance, both y and x were a function of t then we'd have d/dt ln(x) = x'/x.

> I just don't understand why there's a chain rule for lny but not for lnx.
In both cases, you're differentiating with respect to x, so the two aren't equivalent.

d/dx ln(x) = 1/x
d/dy ln(y) = 1/y
d/dx ln(y) = (dy/dx)/y
d/dy ln(x) = (dx/dy)/x

How in the fuck am I supposed to prove this?

[math]A \cup \bigcap B = \bigcap \{A\cup X \,|\, X \in B \}[/math]

Here's what I tried so far
[math]x \in (A \cup \bigcap B) [/math]
[math](x \in A) \lor (x \in \bigcap B) [/math]
[math](x \in A) \lor (x \in \bigcap B) [/math]
[math](x \in A) \lor \forall b\,(b\in B \land x\in b) [/math]

Wtf now. I get a feeling that my definition of [math]\bigcup B[/math] is probably broken

I don’t think the intro book matters so much. Personally I like Gallian and Pinter. And Hungerford is much better than Lang to learn from.

> since the Fourier Transform is its own inverse.

No

My question is math related, but not homework related.
I graduated with a bsc in math from a no name program a little over two years ago. I would like to get a PhD in math so I can teach at a college level, but I'm not sure if I should pursue a master's degree first.
My undergraduate program was small and didn't offer many courses (pic related plus a few electives and an independent study in FEM). Would it be worth while to get my shit together at a master's program before going on to a PhD? The Big 10 in my state offers TA-ships for master's students. Cost wouldn't be an issue, just time.

dx / dx = 1

You take a derivative with respect to a variable.
If you do d/dy[ln(y)] = 1/y.
If you do d/dx[ln(y(x))], you use the chain rule. d/dx[f(g(x))]= f'(g(x))*g'(x) -> 1/y(x) * y'(x)

Bump for interest

This is the chain rule:
[math]\frac{df}{du} \times \frac{du}{dx} = \frac{df}{dx} = f'(x)[/math]

Notice that [math]\frac{df}{du} = \frac{f'(x)}{\frac{du}{dx}}[/math]

which translates to

[math]\frac{df}{du} = \frac{f'(x)}{u'(x)}[/math]

Let f(x) = ln(x) and u=y and you get exactly what you asked for

I learnt this through Calculus Made Easy, and now the chain rule is 100 times easier.

> as other terms appeared out of no where

That's what should happen.

But how to I discern between terms that leave my equation invariant and those which don't?

>How in the fuck am I supposed to prove this?
Unpack the definitions of both side.

a∈A∪∩B ⇔ a∈A OR ∀X∈B a∈X ⇔ ∀X∈B (a∈A OR a∈X) ⇔ ∀X∈B (a∈A∪X) ⇔ a∈ ∩{A∪X | X∈B}