/sqt/ - Stupid Questions Thread

weird stuff happens when you go try to mess with θ > 2pi

its a bit like saying the angles in a right triangle add up to 3pi because pi/2 = 5pi/2

the mistake is to assume that theres only one root. in fact, there are always 3 3rd "roots" and so on, similar to (-2)^2 and (+2)^2 both being 4.
See: en.wikipedia.org/wiki/De_Moivre's_formula#Roots_of_complex_numbers

ohh, i've never heard of that.
the implementation seems weird though.
you are working on the columns of the eigenvector matrix. I think you might want to use the rows, because they actually represent the eigenvectors.
tl;dr use E(:,i) instead of E(i,:)

How do I solve this using laplace transforms? Do I just apply it for each interval, and add the solutions together?

can someone spoon feed to me exactly why an expected value of a random variable is the same as the mean??

I can calculate both, but I don't get the concepts at all

If you don't understand a concept thoroughly, is it better to get stuck with it until you think you get it, or just push on hoping the stuff that assumes said concept is known will make it clearer?

What is the moment equation for the moment about k? Woudn't it be Mk = 0; VL(24') - 4.5 = 0? VL would be 0.187, but the answer my prof says is 0.375.

diffuse thinking nigga

Can you give me a quick rundown?

rundown delivered

Hm it gives about the same result
I think I will leave it there and ask an assistant tomorrow

...

just take a break nigga

Do inertial frames of reference actually exist?

Hi guys, brainlet here forced to take a physics course and struggling hardbody.
>Suppose an object with mass m is projected
with initial velocity v 0 along the horizontal direction. Assume quadratic air resistance of the form F drag = αv^2 , where F drag is the magnitude of the drag force. Find an expression for the velocity v as a function of time.

Here's what I have so far:
ma = αv^2
m*(dv/dt) = αv^2
(dv/dt) = (αv^2)/m
v(t) = integral of ((αv^2)/m))
Am I even on the right track here?

I'm struggling with this question, and I'd appreciate some help, the question is
>Find A and B such that: (pic related)

Usually I would set k to 0 and try to get rid of the variables but that's not possible as they're all powers.

So what I've tried is:
>set k to 0
>Find an equation for A
>set k to -1
>Find and equation for B
>Sub one into other, vice versa

But this doesn't get the right answer when I substitute them back in, set k to 0, and compare with initial function

Any help would be much appreciated

>But this doesn't get the right answer when I substitute them back in, set k to 0, and compare with initial function
show your work

I've got a few permutations of this because I'm not too flash at algebra. I know the answer should be 1/10 but putting this into my calc gives 52/525

Really I just want to know if my process is right

p-p-pls respond

You want to put all the v stuff on one side and the t stuff on the other, then integrate both sides. After your third line you should have

(dv/v^2) = a dt/m

Now integrate both sides and solve for v(t). Do the same for x to make sure you understand.

What you were thinking was not wrong, but since you didn't know how v depended on t, you weren't getting anywhere.

Show that all 5-vertex graphs with each vertex of degree 2 are isomorphic.

so in your equations where does the particle gather speed from?

i never really took a mechanics course but i just did
[math] mg = av^2 [/math]
[math] mg = v^2 \cdot \frac{dv}{dt} [/math]
[math] mgt = \frac{1}{3t} \cdot v^3 [/math]
[math] v = (3mgt)^{\frac{1}{3}} [/math]

Im coming off SSRIs, and I drank last night. Im worried about the interaction. Im reading this

>ssris & alcohol

>Status: Caution

>Note: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

What exactly does this mean? is "denctral nervous system depression" talking about physical reactions, or mental ones? is this basically saying "yeah the combination will make you feel worse" or is it saying it will physically harm your body/ brain?

How should I go about solving b? Do I treat Z(a) as Z(sqrt(-1)) or?

Is there a mathematical way to find the atomic radius of a diatomic molecule comprised of one element?

Atomic radius isn't the right way to describe a molecule.

There is no "hard" radius, even for atoms. At best you can describe a "volume" that the diatomic molecule occupies. That can't be solved mathematically. Bond length, electron density, etc., can only be approximated for any system with more than two electrons. This includes the hydrogen diatomic molecule.

Okay that makes total sense, the line on how I needed v depending on t helped a lot. Here's what I got:
Integrating left side gives me (-1/v)+c and the right gives me (αt/m) + c
Solving for v gives me v = (-m/αt) + C, is this right? By the way I really appreciate the help so far.

I got [math]A=-1[/math] and [math]B=-3[/math].

[math]m \frac{dv}{dt} = \alpha v^2[/math]
[math]\frac{1}{v^2}\frac{dv}{dt} = \frac{\alpha}{m}[/math]

You can use separation of variables or some other autistic math technique to solve the ODE, it should be easy for you

[math]-(v^{-1} - v_0^{-1}) = \frac{\alpha}{m}t [/math]

A little bit of algebra, and:

[math]v(t) = \left[\frac{1}{v_0} - \frac{alpha}{m}t \right]^{-1}[/math]

Great now I'm super confused, so does my post look right at all? To be honest he never taught us anything but simple integral rules so doing this with algebraic expressions with multiple variables n shit is making my head spin.

You have:

[math]\frac{1}{v} = \frac{\alpha}{m}t + c[/math]

Which is what I had ([math]\frac{1}{v_0}[/math] being the constant, the initial velocity). Your next step is incorrect, tho. A small algebra mistake, it should be:

[math]v = \left[\frac{\alpha}{m}t + c{ \right]^{-1}[/math]

*
[math]v(t) = \left[-\frac{\alpha}{m}t + c{ \right]^{-1} [/math]

fuck

Fuck me, you know what I mean. Also, I forgot a minus sign, beware.

SOS

I think I got it. Thanks user.

lads

I cant get my head around the harmonic series being divergent while the hyperharmonics for p>1 are convergent. intuitively it seems that the harmonic series should be convergent because the terms tend towards 0 as n grows

can someone enlighten me

Find them all with an algorithm, and show they are all isomorphic to the first found by trying all permutation matrices.

This result was proven by Nicolaus Osremius in the Middle Ages.

Since 1/n decreases, the sum of 1/n is less than or equal to the sum of

2^n * (1 / 2^n) which diverges.

all this time i thought the nth term test was sufficient to show convergence

thank you friend

>I got A=−1 and B=−3.

Could you please elaborate on how you got this? I tried again and got A=4 and B=9.5. Is my methodology wrong (described above)? I don't think I'm making algebraic errors now.

I'm pretty sure my problem is a shouldn't be using the A and B value from when k is different, but without doing so I can't get simultaneous equations

The functions I have for A and B are:
[math]A = \frac{1}{5}+ \frac{2}{5}B[/math]
[math]B = \frac{-1}{10} + \frac{12}{5}A [/math]

How do I find the critical points of the ORIGINAL function based on this graph of its derivative?

I've managed to solve earlier versions of this problem through making reasonable guesses, although I don't actually know how one would solve this through a recognized method.

I've tried searching for this subject on youtube, but none of the videos are as informative as I would like them to be. They're also of graphs that are not as complex as this one appears to be. Send halp, Veeky Forums, pleesse.

[math] f'(x) = 0 \Leftrightarrow x [/math] is a critical point of [math] f [/math]

How are expected value and mean defined in your textbook?

God fucking dammit will you ever stop spamming this?
x^2+1 is irreducible over Z3 because it has degree

I kinda get your notation. This is Calculus I homework and while I've seen that symbol in symbolic logic I never got particularly adept at it.

Anyway, I eventually figured out the critical numbers are the x-intercepts of the function. Now I'll look for the positive and negative intervals of the original function. Thank you for helping out.

Boundary and isolated points are critical points as well.

What's the equivalent resource for chemistry that the Feynman lectures are for Physics. I'm looking for something readable which means commercial university textbooks are out of the picture.

the stationary points are where concavity changes in the original and the points where the curve = 0 are the stationary points in the original

How do i solve for example 132 = (n! / (n-2)!)

132 = n! / (n-2)!
132 = n(n-1)(n-2)!/(n-2)!
132 = n(n-1)
this holds for n = -11 and n = 12. You want the positive solution

How do I solve this differential equation?

4y''-3y'-y= e^x+x

how i solve this? there is some kind of calculator? first time on Veeky Forums
x + (y * z * t ) / ( y + z + t ) = a

y + ( x * z * t ) / ( x + z + t) = b

z + ( x * y * t ) / (x + y + t ) = c

t + (x * y * z ) / (x + y + z) = d

i tried wolfram but no luck

Use variation of parameters.

>mode
sounds like pseudoscience desu

First solve the homogenous equation (should be ae^x + be^-x/4). Then take the ansatz that the particular solution will be Axe^x + Bx + C, and plug that into the equation, solving for A, B and C. Your solution then is the sum of the homogenous and the particular solutions.

For solving definite integrals with u-substitution, do I ever actually NEED to change the limits of integration and solve with u? Or can I just plug the original expression with x back in and solve with the original limits?

you can do both, but always first try to imagine which result will be nicer to work with after you solve

How do I get good marks in chemistry in general?

learn chemistry

What is the best option for determining attitude in a constantly accelerating object?

An electric car accelerates from rest at a rate of 3 m/s^2 until its speed
is 30 m/s. It then slows down at a rate of 2 m/s^2 until it comes to a full stop.
Find
(a) The total elapsed time from the initial stop to the final stop.
(b) The total distance covered in this time.
(c) The average acceleration of the car for this time interval

How do I answer c? I have an answer but i feel like its a trickier question

Why is young's modulus so small for this tensile test? Material is brass, CES Edupack states values should be within 90 and 110 GPa.
Is there an additional calculation I'm missing?

strictly, I'd say zero, as decelerating is negative acceleration. If it about absolute acceleration it's probably just (10*3 + 2 * 15) / 25 = 2.4 m/s^2

Isn't that a non-homogenous equation though?

Yeah, but for solving a non-homogenous equation you still need the solution to the homogenous problem as part of the solution.

I take zoloft and still binge drink during college nights out. It's fine

How do I "learn" """chemistry"""

ssris potentiate the depressant effects of alcohol for some people.Basically, 'you might get drunker faster'.

I knew frogposters were dumb, but man are you dumb.

What is an intro to real analysis course like? The description for the course I'm taking next semester is : The Completeness Axiom, Sequences, Series, Absolutely and Conditional Convergence of Series, Power series, Cardinality of sets, Continuity and properties of continuous functions.
Boundedness Theorem and Intermediate Value Theorem

A lot of these seem to Calculus 2 topics

That's not a real analysis course

what is it then?

What method should I use to find a differential equation with the solutions e^x, xe^x, xe^-x, x^2e^x ?

some random assortment of calc 1 and 2 topics

look up graphs of functions and their derivatives. From f(x) to f'(x), extrema become zeroes and inflection points become extrema. The reverse holds true so just work backwards.

No I get im supposed to learn it, but what about tests? How do I do well on those? Im good at understanding concepts but the tests anal me every time

I do not understand the math behind this, is it implied that A/(1-b12*b21) results in a scalar?

>good at understanding concepts
>tests anal me
Then you're not understanding it. Study more desu

do practice problems. your professor doesn't really care whether you understand shit, as long as you get the right answer.

Yeah I guess not. I get the general idea really easily but then the test has really specific problems, so ill have to do a lot of abstract problems to better prepare

No, but the matrix multiplication A with that other matrix does result in another 2x2 matrix.

So each phi is a new 2x2 entry of this matrix?

each phi is another matrix for the sum. The phi11(i) etc. is just the top-left entry of the i-th phi matrix.

Oh, thanks for your patience.

>That's not a real analysis course
this autist

>this autist
The entirety of those topics is covered in probably ~20 pages in any real analysis textbook.

>my book where we covered abstract metric spaces was called real analysis, therefore only metric spaces are real analysis

How do I take apart a three dimensional vector? It's hard to visualize on paper.

>>my book where we covered abstract metric spaces was called real analysis, therefore only metric spaces are real analysis
Who are you quoting?

Given two pentagonal numbers [math] P_n=\frac{3n^2-n}{2} [/math] and [math] P_m=\frac{3m^2-m}{2},~n>m>0 [/math], when will their difference also be pentagonal? I know that $n-m$ has to be odd, is there anything else we can conclude?

Oops, meant [math] n-m [/math]