/sci/ - Science & Math

I'm trying to synthesize WS3 to do things with later, but all I have is Na2WO4(H2O)2 for a tungsten source and then thioacetamide (C2H5NS) and Na2S for a sulfur source. I have access to any acid or base that would be necessary. Right now I'm trying to take the sodium tungstate and add 3M HCl to make it WO3 and then remove that and add Na2S and mix to substitute the sulfurs, however I'm getting some blue crystals that are also forming so I'm trying to figure out if there's a better way to do it or if I just need to make sure it is completely dry before adding Na2S?
other chemfags help would be appreciated

>>10042531
a winnar is you for that photo

Is there a notation for the set of all (Lebesgue) measurable sets?

Um so in a lot of introductory proof (based) books they say you should ask a professor for reassurance for some of the open ended questions... how the fuck do I that? Do I just pretentiously walk up to my linear algebra professor and ask him to help me with material that's unrelated to the course?

>>10042824
that's what office hours exist for
>"hello Dr. Anon, I was going through the book and came across X. My understanding of it is Y. Would you say this is accurate?"
if you don't want to open with your own question, find something from the lectures to probe about first (preferably you know the answer to this already so you don't look like a moron), then ask the real question.

>>10042531
>that guys head is caved in

so how come he isnt dead?
is he now mentally retarded?

>>10042803
The Lebesgue [math]\sigma -[/math]algebra, which is also sometimes denoted [math]\cal{L} (\mathbb{R})[/math], or more generally [math]\cal{L} (\mathbb{R^{n}})[/math]

>>10042824
Yes, all non-jaded professors love students asking intelligent questions.

>>10042852
>>10042858
O-okay. I'll go with the first anon's approach and segue into the non-related book. Fuck I hate the initial encounters with professors.

>>10042866
Most professors are actually very happy to discuss their field with interested students, because most of the students they deal with day in and day out are apathetic, unmotivated undergrads looking for the answers to some entirely procedural question.

>>10042879
I understand that, I've even seen that myself a few times but I still usually assume that my professors hate me even when they say otherwise. It doesn't matter though.

>>10042853
Had the accident when he was 14, thus his brain adapted. Not retarded, but not bright to begin with, given he was driving while high, and underage (or well, at least not wise - kind of amazing how many super-intelligent druggies and daredevils there are).

You can lose half your brain and continue to function relatively normally, particularly if the brain matter isn't lost, but compressed, which was largely the case here. There's been instances where folks have lost 90% of their brain compressed into 10% of the original space, due to conditions pushing the gray matter into tight areas, yet they seem relatively normal. On top of that, outright removal of nearly half the brain is a standardized (if rare) procedure for dealing with severe epilepsy - which has been done on people as old as 19, with no impact to IQ. (Though it has some other effects that, while very odd, aren't necessarily terribly debilitating.)

>>10042912
my understanding is if you get half your brain taken out at a very young age there are incredibly few and sometimes no discernible symptoms bythe time you mature.

>>10042912
>outright removal of nearly half the brain is a standardized (if rare) procedure for dealing with severe epilepsy

if you had that procedure what would they put inside your skull to keep the good half of your brain from flopping around?

>>10042929
that question doesn't belong in this thread

Anyone here study in the UK? I'm in Canada and thinking about studying abroad for my masters (1 years+summer vs 2 years in NA). How are the universities? I don't mean major ones like oxford or cambridge, but smaller ones like Keele. What major/university are you attending in the UK? Do you enjoy it? Thanks.

>>10042531
Why do physics majors have higher IQs than Math? Is it because Physics requires more modelling and relations to actual phenomena?

If smelling an object removes atoms from it, how many times would you need to smell a piece of bread before it stops existing?

Intuitively, I know what different temperature values mean. 21°C is comfortable. 30°C is hot. 10°C is chilly. 0°C is cold.

What about humidity? If my room's air has 62% humidity, wtf does that mean? I saw a website that vaguely describes 60% as the upper comfort limit, but I don't think that's true

So I took my first real analysis exam, and there was a problem that went as the following:

if [math] |a - 10| < \varepsilon < 1 [/math] then find [math]N[\math] such that [math] |a^100 - 10^100| < N\varepsilon [\math]

I used triangle inequality in the forward direction i.e [math] a^100 + 10^100 [\math] and multiplied by [math] \frac{a^-99 - 10^-99}{a^-99 - 10^-99} [\math] so that I could get [math] a - 10 < \varepsilon [\math] on the top and then use the fact that [math] a < 11 [\math] for the denominator.

Was my method here correct? I couldn't think of anything else besides some yucky binomial expansion trick.

>>10043172
I'm not sure I'm understanding correctly, but if I am then check the numerator twice.

>>10043158
If it did, it'd depend on the mass of the bread.

But it doesn't. Your nose just picks up shit in the air. So, however long it takes you to snort the piece.

>>10043133
Depends where you go to and what you do obviously. Also there's a difference between campus and city universities. Overall you don't have the "general education" aspect of american universities, so you will focus much more on your major.

>>10043142
because math is taken by people who wanna be math teachers (math education) and by women for whatever reason (around 40% of undergrads are women), so it is inevitable the IQ is gonna go down

>>10043172
[math]|a^{100}-10^{100}|=|(a-10)(a^{99}+10^{99})|<\epsilon |a^{99}+10^{99}|[/math] so choose [math]N[/math] bigger than the last term (which exists by Archimedean property.

Brainlet

theres this problem I dont know how to do, anyone know?
a particle of mass [math] m [/math] and charge [math] q [/math] is moving under the influence of an electric field [math] \vec{E} [/math] thats perpendicular to a magnetic field [math] \vec{B} [/math] in the [math] XY [/math] plane with constant velocity [math] \vec{v} [/math].

they give you values for all things and make you compute the magnitude of [math] \vec{B} [/math] which turns out to be [math] 2.6187T [/math]
and they they tell you a new magnetic field [math] \vec{B_1} [/math] is added in such a way that the particles velocity doesnt change. then youre asked to find the maximum values [math] \vec{B} + \vec{B-1} [/math] can take.

how the fuck do I do this? sum of all forces = 0 is useless cause I dont know the angle the velocity vector forms with the new field

please help

I know this is a really, really stupid question, but why is the negative vector originating from the point? Why doesn't it originate from the -q charge and point in the opposite direction from the +q charge?

>>10042531
Why tf are complex numers a thing when you cant pull the squareroot out of -1? I can count with that crap but why tf is this shit there?

>>10043326
It's like a shortcut.
You can skip complex numbers and calculate using sines and cosines if you wish.

>>10043326
complex numbers mean something different than real numbers.
theres a whole youtube series about this topic i recommend watching, its called imaginary numbers are real.

>>10043313
>q is moving under the influence of an electric field E⃗ thats perpendicular to a magnetic field B⃗ in the XY plane with constant velocity v⃗


That's not possible imo due to the lorentz force.

I'll study etech soon and am preparing since weeks in math. I know almost everything but still fear the worksheets since I already failed a semester of pure math. Still got 5 days for preparation. How shall I cope with the fear? I want to be as good as possible.

>>10043356
lorentz force just equates to 0 in that case.
so this holds:
[eqn] E = qB\sin{(\varphi)} [/eqn]

the problem i have with this thing is that a magnetic field cannot change the speed of a charged particle, it can only change the velocity, so if B1 doesnt change the velocity then B1 must be in the same direction as B and if its in the same direction as B, the sum of the magnitudes can be infinite and the velocity will still be unchanged.
theres got to be something i dont know/understand here.

living is just killing time before death comes

>>10042912
why is /sci/ so OBSESSED with age?

>>10043380
How? You said the E field drives the charge, B is perpendicular to E. Thus the lorentz force should not be equal to 0.

Draw a scetch.

You also seem to confuse velocity and acceleration.

why do physics and math profs be writing x like )(

anybody else know what im talmbout

>>10042912
so the visual representation of brainlet memes is actual bogus?
nice

If two people play a game which is best of X rounds, and you know the probability that a player will win the whole game, can you reverse engineer the probability of that player winning a single round?

>>10042852
>>10042858
So I actually went to his office hours today and he was very smug and dismissive. He had this shitty smirk on as soon as I walked in and looked at me in disgust when I asked a question about a part of a proof. He seemed insulted. Never again. I could tell from our lectures that this guy is a dick.

>>10043424
I didn't say the E field drives thw particle, I said the particle is traveling thru a region with an E field and a B field

>>10043245
I think he wants to know how long it would take for a piece of bread to sublimate.

>>10043322
Another really stupid question, why does he multiply by cos? I understand why he only wants the vertical component, but how does multiplying by cos get us that?

>>10043440
yes, very easily

How do you compute the odds of winning in "system" lottey picks?
I.e. assuming a 6/58 lottery, instead of picking 6 numbers, you can do "system 7", picking 7 numbers instead and you can use any 6-combination of the 7 numbers to match to the winning lottery numbers.

could one find the solution to the proof based exercises in Apostol's calculus?

how do you even self-check proofs if you're self-studying anyways

What is energy made out of?

>>10043440
The probability of winning a set of rounds is exactly equal to the probability of winning an individual match

I would love to eat some fruit loops off his head

>>10043303
but is my logic wrong?

>>10043947
nothing inherently, it can be made out of anything

the defining aspect is that it's conserved

>>10042531
Is he allowed to drive legally? How does that even happen?

Ok folks. I cannot get D and I feel like a retard. help pls

>>10044544
It's e^2 I understand now

Tried asking this in the previous thread but noone answered me, maybe I'll get lucky this time around. Why does GAP do this with variables but not with lists?

>>10042531
Good-day! W-what is the function of the Laplace transform? I've been going through the PDFs numerous times, memorizing the formulas and trying to focus on the actual text though can't really get to grips with it. So there's a function that turns an input into an output designated as L(x) and creates an integral between infinity and 0, how does that make a causal function such as u(t) turn into 1/s? Where does the "s" even come from and why does the "t" disappear? Furthermore why do "a"s get shoved into the powers on hyperbolic functions e.g. sinh, cosh, tanh? That just seems rude.

Let's say we invented a machine that works out where every particle in the universe will be according to physical determinism, so you could see the future exactly. What happens if you try and change that future?

>>10044688
Ignoring the impossibility, you'll find you already changed the future... Also your head will explode.

Focusing on the small string element shown in the insert of the figure, show that the angles α
and β satisfy

tan α =dy(x,t)/dx and tan β = dy(x + ∆x, t)/dx

I am not sure how to start this, it has been a long time since I have done proofs. What is the general outline to show this?

>>10044677
>Where does the "s" even come from and why does the "t" disappear
It's a change of basis from the time domain to the s domain.

spoiler: s is just γ+i*ω = 2πi*f+γ aka the frequency domain with an arbitrary fug factor γ to make the integral converge for periodic functions like sin(t)

>Furthermore why do "a"s get shoved into the powers on hyperbolic functions e.g. sinh, cosh, tanh? That just seems rude

You mean [math]inverse[/math] power of hyperbolic functions? Because its like "arc" for trig functions but "a" for "a"rea.

>>10044772
>A filter [math]\mathcal{F} [/math] on [math]X [/math] is an ultrafilter iff for all [math]E \subset X [/math] either [math]E \in\mathcal{F} [/math] or [math]E^c \in \mathcal{F} [/math].

Is it obvious here that [math]E^c = E\setminus X [/math], or do I need to somehow make it explicit? if I do any suggestions? (I want [math]E^c[/math] because it makes the proof look more elegant).

>A filter [math]\mathcal{F}[/math] on [math]X[/math] is an ultrafilter iff for all [math]E\subset X[/math] either [math]E\in F[/math] or [math]E^c\in F[/math].

Is it obvious here that [math]E^c=E\setminus X[/math], or do I need to somehow make it explicit? if I do any suggestions? (I want [math]E^c[/math] because it makes the proof look more elegant).

>>10044677
I used it in the context of differential equations, it's pretty useful to solve some of them. Since they will get a simpler form after applying L(x) to the equation, you solve them there and do the inverse transform on the result.

To get the transforms you do the integrals, but there's usually tables for the most common ones, do 1 or 2 as an example and use tables after

>>10044795
Thankyou for the information, I think I'm getting it now though what is a fug factor? It made me giggle slightly though that is an unknown concept to me. Really cleared up hyperbolics for me though, don't know why I kept forgetting to put inverse.

>>10044806
Great clarification, I'll try to apply them more towards differentials then in a bid to integrate it into my brain better, I've seen the main table and know about half of the values thus far though I'm working on memorizing it by the end of today and being able to properly apply it.

if you're on a plane with an open top and had the ability to jump high enough that you would exit the cabin into open air, would you still land back in the plane?

>>10044815
>fug factor
*fudge factor, basically you're multiplying the function by e^-γt just so the integral converges.

>>10043966
I don't understand this. If a player has a 60% chance of winning a single round, and they play best of 99, surely that player has a much larger chance of winning than if it is best of 3.

>>10044832
Is that so? Thanks for the additional clarification.

>>10044804
the complement is only defined when considered as a subset anyways, so if the context is right, then you should be able to write it without confusing the reader

>>10044824
if there was no air, yes. But you are not as aerodynamic as the plane and you're not accelerating in its direction, so you would instantly lose speed and miss it

>>10043322
>>10043500
Bump?

>be me
>be very good at calc 1, 2, and 3
>be very good at diff eq
>currently failing linear algebra
What the fuck? Is this common? Is there any supplemental reading I can do? For some reason I can't grasp the concepts beyond solving Ax=0 or Ax=b, etc.

>>10045037
think geometrically or read a book that is proof based like LA done right by Axler

>>10045037

http://joshua.smcvt.edu/linearalgebra/

>>10045037
my friends also all struggled with linear algebra yet were good with calc, it seems to be a common thing. I think the problem is that lots of people dont get the geometrical part, and a lot of profs never teach it. Like my friends struggled with the definition of a subspace for a long time, yet I (and I heard another student also explaining it like that) could see that its a flat slice through the origin, if you think about it like that its a lot easier to see why its defined that way and a lot of proofs are a lot easier than when you only look at the equations, and my friends also understood it better after I told them that.

>>10044677
> W-what is the function of the Laplace transform?
It turns differential equations into algebraic equations.
L(dx/dt)=s*L(x)-x(0)
Once you've rearranged the equations to get L(x) as a function of s you apply the inverse transform to get an explicit (closed-form) expression for x(t).

> how does that make a causal function such as u(t) turn into 1/s? Where does the "s" even come from and why does the "t" disappear?
It's a change of basis. The s is a free variable, the t is bound. It's similar to linear algebra. E.g. you can transform any <x,y> to <u,v> where u=x+y,v=x-y without losing information. Similarly, you can take an infinite number of <t,f(t)> pairs (i.e. a function) and transform them to an infinite number of <s,F(s)> pairs (a different function), where each F(s) depends upon every value of f(t) for t>=0.

A matrix transformation y=M.x is just a sum of products:
y[i]=sum[j](M[i,j]*x[j])
The Laplace transform is the same but the matrix and vectors are (uncountably) infinite:
y(s) = sum[t](M(s,t)*x(t)) where M(s,t)=e^-st.

> Furthermore why do "a"s get shoved into the powers on hyperbolic functions e.g. sinh, cosh, tanh?
If you take several functions of t with the same structure but different coefficients, their transforms give you functions of s with the same structure but different coefficients.

The only transforms you need in practice are L(dx/dt)=s*L(x)-x(0) (higher-order derivatives can be obtained by repeated application of this rule) and L(t^n*e^-at)=n!/(s+a)^(n+1). Everything else is just Euler's formula (e^ix=cos(x)+i*sin(x)) and partial fractions (so that you can break down arbitrary rational expressions into k/(s+a)^n terms).

>>10043163
Humidity influences condensation and the ability of the body to cool with evaporation.

Look up the dew point temperature which indicates which temperature would have 100% humidity with the current amount of water in the air.

>>10044672
Because lists are probably references.

Imagine that the variable actually holds a number which points to one of the saved lists in a big numbered collection of those lists.

So you have Lists:
1: (a,b,c)
2: (d,e,f)

List-Variables
i = 1 -> points to (a,b,c)
j = 2 -> points to (d,e,f)
j = i -> j = 1 -> points to (a,b,c)

Perhaps?

>>10044688
Maxwell's demon would have to be metaphysical, otherwise you get a liar type paradox when two of them try to predict each other.

>>10043142
Because physics teachers are dicks

Why does it seem like the kids in the math club know everything? Did they get a rigorous summary of calculus in real analysis or something? They seem to have retained every little detail of early undergrad. Fuck I feel so inadequate around them, even as an intended major.

Is it weird if I list myself as "Research assistant" for a paper I'm submitting for publication?

This journal is weird that it asks for everyone's current roles and I wrote it while I was doing my Honours. I'm not in any academic role at the moment (i.e. it's not like I can list myself as PhD candidate) and I'm really just doing research assistant work.

My co-authors and supervisors are solid names in the field so I'm not worried about my paper not sounding legit or anything, just wondering if it's weird.

How bad am I fucked for EE grad school if I got an F in an upper division class then retook the summer right after and only got an A-? The reason for the initial F is pretty run of the mill. I had mental health issues and didn't finish the final project.

My overall GPA is around a 3.7, not counting my CC grades (have a C+ in another upper div course) and my major GPA (just upper divs) is a 3.87.

Assuming I have decent research and good LoRs, will that F bar me from top 50 schools? I go to a not-so-good State U, too.

>>10042531
Why are engineers such awful people and why do mathematicians have such a good sense of humor? What gives?

Are there any analytic solutions for 1 dimensional equations of motion that are bounded OTHER than the harmonic oscillator? I want a position and momentum pair that obey a nonlinear set of DEs but I want them to remain bounded and stable.

>>10046011
some universities just scrub it from your record on the first retake

>>10042531
do i have dyscalculia? i find it really hard to do basic math in my head and algebra is impossible for me

Is there any point in studying calculus?
Taking my last year of calc which is just 3d stuff, but I feel like I won’t really use this stuff irl. i’m an ee major.

>>10043322
negative charges are sinks, therefore the e-field at the given point due to -q will point towards -q. the middle vector is the net e-field due to both charges. study the basics behind e-fields

>>10043142

does this normalize for the number of people intending for each major?

>>10046441
Pretty much all physical processes (including electrical) are modeled by calculus. Signal processing heavily leans on calculus I'm surprised you don't know this yet.

>>10046456
I guess I’ve used differential equations for solving stuff like circuits, but it still feels like a majority of the stuff is irrelevant. When am I going to need to calculate where the steepest slope is for a mountain or find a tangent plane?

>>10046300
Just put the the object in a potential well of some sort. Haronic has U = x^2, Try U = x^4

>>10046462
Optimizing a function of two variables.

>>10045037
unironically watch 3blue1brown's series on LA
I had to take the course online, so I wasn't making a lot of important conceptual connections from unit to unit.

>>10043500
draw your free body diagrams

Can an undergraduate do a DIR course under a graduate professor at the same university?

Is it possible to get into a good graduate program on GRE scores alone?

Doing discrete math and stuck in a very simple problem.

What would be the negation of:
X is a cow, and either Y or Z is a bird

>>10043142
>Religion
how

>>10046508
have you ever taken an intro to religion class? They're pretty though provoking

>>10042929
Silicone was used at least one time, but generally they leave the space empty and it fills with cerebrospinal fluid.

https://en.wikipedia.org/wiki/Ahad_Israfil
http://www.c3.hu/~mavideg/jns/642696june1.html

if sets [math]A,B[/math] are open in some topology, and [math]A\cap \overline{B} \ne \emptyset[/math] then does [math]A\cap B \ne \emptyset[/math]?

>>10046499
P=X is a cow
Q=Y is a bird
R=Z is a bird
[P and (Q or R)]
By DeMorgan's law, the negation is
not[P and (Q or R)]
notP or not(Q or R)
Again, by DeMorgan's law:
notP or (notQ and notR)
In other words
Either X isn't a cow or Y and Z aren't birds

>>10046499
not (X is a cow, and either Y or Z is a bird)
(X is a not cow) or not (either Y or Z is a bird)
(X is a not cow) or not (either Y is a bird or Z is a bird)
(X is a not cow) or (either Y is not a bird and Z is not a bird)

>>10043142
>philosophy
damn it feels good to be a gangster

>>10046525
B is (not strictly) contained in its closure because the latter is just the intersection of all the close sets that contain B. Then, if [math]B \subset \overline{B}[/math] and [math]A \cap \overline{B}[/math] is empty, there can't be any elements in [math]A \cap B [/math], since then they'd necessarily also be in [math]A \cap \overline{B} [/math]

>>10043163
it matters bc the humidity changes the specific heat of the air arround you, making harder to achieve the confort temperature that your body tries to get. It works in either way (too cold and too hot). You would probably feel colder a 10°C temperature with a 100% humidity than 3°C with 30% humidity.

>>10046012
engineers tend to do it for the money, while mathematicians are passionate about their subject, so clearly many engineers are bitter

>>10046552
read the question again bucko

>>10046525
consider the real line with the usual topology, A=[0,1], B=(1,2)

>>10046597
[0,1] is not open

>>10046607
Oops yeah didn't see that
>>10046525
If x is a point of closure of B, then every open neighborhood of x intersects B nonemptily. Since in particular, A is open, then A intersects B nonemptily

alright i posted this problem on here a few days ago but there was some problem with the site.
i need a way to prove that [math]\frac{a}{b^2}+\frac{b}{a^2}\geq\frac{1}{a}+\frac{1}{b}[/math] for any a,b

>>10046791
i should probably mention that the textbook says to use the identity proven earlier [math]a^2+b^2 \geq 2ab[/math]

>>10042961
Why? Because it's not stupid?

>>10046791
>i need a way to prove that [math]\frac{a}{b^2}+\frac{b}{a^2}\geq\frac{1}{a}+\frac{1}{b}[/math] for any a,b
It's not true.

>>10046833
counterexample plz

>>10046844
Consider a=0.

>>10046850
good point, the problem definitely says for any a,b. might have to leave this one blank then.

>>10046478
>DIR course

"Directed Independent Reading" course? Yeah, many universities have "49x independent studies" placeholder course for just that.
https://en.wikipedia.org/wiki/Independent_study

Speak to professor, speak to the department(s) you want the credits to count for (major elective, technical elective, and/or general elective), and sign up for it.

>>10046499
Not "X is a cow, and either Y or Z is a bird" :P

>>10046508
You have to be over the age of 18 to post here.

>>10046868
In order for that statement to be true, you need (a^2-b^2)(a-b) >= 0, which does not hold for all a, b not equal 0. For example, a=-1 and b=1/2

>>10043142
because physics is a description of the real world

I have a lotto question and its picking 6 balls from 45 (1-45) so the odds are 1 in 8,145,060

if u have 20 games is it written as 1/8145060*1/20 odds? or is there an actual 1 in x odds of winning?

or is it expressed as 20 in 8145060?

>>10047074
If [math]p[/math] is the probability of winning a game, then [math]1-(1-p)^{20}[/math] is the probability of winning at least one of the 20 games.

Which one is the phase portrait, and which one is the vector field? Both of those terms were introduced at the same time and they both refer to this graph in the text that I'm reading.

So, the phase space is where all the trajectories (solutions) to a problem are. Does this mean that f(x) is the phase portrait and the vector field is the arrows on the line?

>>10047140
Isnt it ((1-P)/P)^20?

That gives 20 games as 0.9999975445
> * 100 = 99.99975445% chance of losing
> 1 - 0.9999975445 = 0.0000024555
> 1+ 0.0000024555 =
> 1.0000024555 in 8145060 odds if 20 games are played

What if there are 2 supplementary numbers drawn - if they are both between 1-10 (or whatever supplementary numbers are normally used) how are they removed from the original odds and included in the 20 games?

I can find notes on extra numbers (such as seventh ball being between 1-15) on top of the picked 6 but nothing on removing the odds from having 2 supplementaries

>>10047225
>> 1 - 0.9999975445 = 0.0000024555
>> 1+ 0.0000024555 =
>> 1.0000024555 in 8145060 odds if 20 games are played
scratch that part wtf

Anyone able to offer some insight to pic related? On top is the question, bottom is the process I've tried. I keep getting that transmission = 1, which is definitely wrong. I suspect something is wrong with the sinh function, but beyond that I'm not sure.

>>10047312
Update: I've found that with these L and M values, as long as E and U exist, T will always equal one. That's still incorrect, so any help is still appreciated.

When dividing two numbers, can you tell the number of digits in the quotient without actually doing the division yet?

>>10045037
two points define a line
three points define a plane
two intersecting lines define a point
two intersecting planes can define a point, or a line

Understand these and translate them to equations and matrices.

>>10047312
I think you just need to check your formulae. I'm looking at my copy of Zettili's Quantum Mechanics Concepts and Applications, and these are the coefficients derived there.
Here [math]k_1 = \sqrt{2mE / \hbar^2}[/math], [math]k_2 = \sqrt{2m(E-V_0) / \hbar^2}[/math], a is the barrier width and V_0 is the potential of the barrier.

>>10047775
Sorry, I made a mistake in copying these from the book. k_2 should have V_0-E and not the other way around. Anyway, these should be equivalent to what you're using.

I think your >>10047312 mistake is in using the wrong units for one of your quantities. I converted all values into SI units and got roughly T = 0.07 and R = 0.93. The problem is in your q constant. I got around q=1e10 when using SI units.

Is there a way I can quantify the level of diversity within a population as a single number?

For example, if population A was made up of
>5% red
>5% green
>5% purple
>5% yellow
>80% blue

and population B was made up of

>20% red
>20% greed
>20% purple
>20% yellow
>20% blue

..one would say that population B was more 'diverse' than population A, but is there a formula that enables me to express this as a number?

>>10047935
Standard deviation of all the percentages

>>10047559
If the dividend has M digits and the divisor has N digits, the quotient will have either M-N or M-N+1 digits. If the number formed by the leading N digits of the divisor is greater than or equal to the dividend, the quotient will have M-N+1 digits, otherwise M-N digits.

>>10047935
Look up "diversity index" on wikipedia.

>>10047986
Cheers, I thought as much.

Does this look good?

>>10048034
Well, I suppose what I'm really looking for here is a measure of how un-homogeneous a group is, rather than a measure of how close the diversity of a particular sub-group is to a wider group (for example of a city within a country).

There are these pistols that use a system called gas-delayed blowback.
As seen in the picture, there is a little port on the underside of the barrel that bleeds the expanding gases from the explosion into a separate chamber beneath the barrel.
Supposedly there is much more heat and pressure in the chamber than there is in the barrel.

Why is this? Why doesn't the high pressure gases that have been leaked in the chamber go back to the barrel to equalize the pressure?

>>10048455
I doubt that the heat and pressure inside the chamber ever exceed the heat and pressure inside the barrel
but it is possible that the heat and pressure inside the chamber remains for longer.
The chamber is open only by a tiny pipe, while the barrel and the ejection port leave a large area for gas to escape from.

>>10048455

IDK for sure, but

the expanding gas is forced through the small port then the venturi effect means gas achieves higher velocities

The dimensions of the chamber and the capacity of the expanding gas is calculable by the energy in the charge.

These guarantee that the expansion will complete its mechanical action of pressing the spring by the time the bullet leaves the chamber and escaping gas pressures equalize between both chambers.

>>10047896
You were right, it was a unit mismatch. Changing from eV to J fixed it. Thanks.

>>10048546
small correction
pistols eject based purely on the recoil caused by the expansion of gas--no spring necessary.

the spring is only to bring the action--and a new bullet--into the chamber, locked and loaded.

the chamber is actually used to slow down the blowback or ejection, hence delayed blowback. developers claim dramatically reduced felt recoil by users.

>>10042531
Why is science respected when all scientists aren't required to be logicians? If they're not logicians, how can we trust their inferences, peer-reviewed or not by other people prone to the same logical mistakes? Think of it like a bunch of children using the scientific method and reviewing each other's findings. Would you trust them?

>>10046481
pls respond

For which values of z does the series (sum from n = 0 to infinity) (1/(n^2 + z^2)) converge?

complex analysis

Is there an easier way to show this instead of just doing the algebra? I've been working at it for a few hours and I can't figure it out

Can supercooled conductors emit "controlled" waves in the visible light spectrum and above?

>>10048741
Linear algebra and you don't have to be the one to do it, or row reduce it by hand if you refuse to use software, less thinking and more formulaic.

>>10048717
>For which values of z does the series (sum from n = 0 to infinity) (1/(n^2 + z^2)) converge?
What have you tried?

>>10048761
I haven't taken linear algebra in 3 years but I knew there was some way to use it to solve it, thanks a ton, I just figured it out using a row reduction tool online

In a pitch black room, is white or black clothing warmer? Would the black clothing absorb the heat from your body and make you warmer, or would the white clothing reflect the heat from your body and make you warmer? Or are both of these scenarios ridiculous and unfounded?

>>10048835
White would be warmer because it's a radiative insulator.

>>10048847
that makes sense, thanks!

Can someone redpill me on the transition of electron degeneracy pressure to neutron degeneracy pressure??

Will probably just start a thread about it if I get no (You)'s

>>10048770
Well I know for sure it's divergent on z^2 = 0, -1, -4, -9,... since that has undefined values.

I split it into

(1/n^2)*(1/(1+z^2/n^2)) and tried to show that (|1/(1+z^2/n^2)) is convergent but am having troubles finding a lower bound.

>>10048992
hoping for help on this still,

like I know if

(|1/(1+z^2/n^2)|) > 1/2
then
|1/(n^2 + z^2) <= 1/n^2 and by the comparison test it's convergent

The teacher in my upcoming complex analysis class is an engineer. How fucked am I? Should I drop the class for another one?

>>10048654
I DONT KNOW BALLOON MAN :(

If [math] M \in GL_n(\mathbb{C}) [/math], what are the matrices [math] A \in M_n( \mathbb{C}) [/math] such that [math] M = A^t M A [/math]? Taking the determinant of both sides gives me [math] \det(A) = \pm 1 [/math] and obviously [math] A = \pm I [/math] are valid solutions. I can't seem to deduce anything more than that.

>>10049368
I should clarify that by [math] A^t [/math] I mean the usual transpose (not the conjugate transpose).

>>10046481
yes, it is possible

Brainlet here
What is the basic pathway to learn more advanced maths?
Calculus - Differential Equations - Partial Differential Equations? Wiki isn't really clear
I want to have a solid math background to not feel stupid when I get some hard shit.
I feel pretty confident about high school shit, the resources in the wiki helped a lot.

>>10049576
you want to learn single variable calculus then multivariable calculus obviously. differential equations is basically just antiderivatives (sort of). there are two types:
1. ordinary differential equations - differential equations of one independant variable
2. partial differential equations - differential equations of more than one independant variable

really this all falls under the banner of "calculus", it's just that universities like to split calculus courses away from differential equations and put them at a higher level because they can get quite involved.

>>10049368
So playing around with it a bit it becomes clear that the set of matrices that have the desired property form a group, i.e. the inverse satisfies the properties and it's closed under multiplication. So we're looking at some subgroup of the special linear group. (I know that's not technically true, we're looking at a subgroup of two copies of the special linear group). There's also something interesting about M, namely if you take the transpose of both sides it's not hard to see that the matrices A that you want also satisfy the same property for M transposed. I've only gotten this far so far, but I'm more inclined to believe that the set of matrices either all of the special linear group or is trivial.

>>10049576
>basic pathway
It branches out and cross pollinates

Learn proofs
https://4chan-science.wikia.com/wiki/Mathematics#Proofs_and_Mathematical_Reasoning

Then read an overview book to get a sense of subject
https://4chan-science.wikia.com/wiki/Mathematics#Overview_of_Mathematics

>>10048654
The single most important thing for getting into a graduate program is your letters of rec. Then it's your undergrad transcript. Taking the GRE is mostly a formality. Schools only use it if space is filled up and they need to decide between two similarly qualified applicants.

>>10050253
What if I get a perfect GRE score but only have a 3.2 GPA? What kind of programs can I get into?

>>10045037
>linear algebra
HAHAHHAHAHA.
Ok you are failing it, not big deal, but just get the matrixes dude. It makes sense to me actually calc is easier for some.

I am coursing calc 2, algebra 2 and physiscs1 since August 20. They seem easy enough by now (not passing them though cause i dont study and have not memory). Does it get more difficult?

>>10050800
>calc 2, algebra 2 and physiscs1
>algebra 2

Wut? Is that some numerical linear algebra course or something?

>>10042586
what year is it

Is Julia a good alternative to Matlab?

>>10050876
Only if you compile it without the GPL libraries.

Question is to determine if W is a subspace of V.

I don't understand the notation? Is W the set of all real functions with domain in [a,b] and codomain in R?

>>10051055
Functions from [a,b] to R

>>10050112
Thanks for the reply. When M is a scalar matrix, we get A^t A = 1, so that gives the orthogonal group. I'm starting to think there might not be simple description of the group for arbitrary M.

is it really dangerous to daisy-chain several power boards or extension leads together? why?

>>10051170
you know the reason they never recommend daisy chaining extension cords together?
because extension cords have shitty insulation and thin wires.
causes voltage drop over long distances and overheating aka housefires.

>>10051182
all right in other words there is nothing wrong with the connection itself so if high quality extension leads are used that would eliminate the risk, wouldn't it?

How do I prove that the equation:
(x − 1) sin(πy) = 4y − 1

only crosses the y-axis on one point?

>>10051700
Set x=0 and solve for y but I don't think that's gonna work here. I think you might have to like use the power series for sine and divide out the y somehow so you can solve for y. Or something else.

>>10051710
Yeah, that's what I'm struggling with.
I set x = 0 av showed through the mean value theorem that the graph crosses the y-axis at least once, however I can't show that it only does so once.

The implicitly differentiated doesn't really help here either.
However, I know I have to show that the graphs is strictly decreasing in the interval, thus proving it can only cross the axis once. (So Rolle's Theorem)

>>10051055
https://www.google.com/search?q=set+builder+notation
https://en.wikipedia.org/wiki/Set-builder_notation

Could you generate Earth-like gravity on other astronomical objects using the same approach as for rotating space stations, but with a conical ring so that the gravitational force of the object and the centrifugal force of the rotating ring create a resulting force perpendicular to the ring's surface and equal to Earth gravity?

>>10051170
No. Its mostly to get out of warranty coverage and some of them have shitty ground connections that will cause the rest of the chain to be ungrounded.

>>10051182
>causes voltage drop over long distances and overheating aka housefires.

Only a worry of you coil the wire up on itself.

>>10051221

Some retards chain 14awg -> 18awg -> 14awg and try to draw 15 amps. Linked cables are only as good as their highest gauge.

>>10051724
Yes you could but it would suck. If you live on a planet you want to walk around an explore the alien mountains and rilles and shit. If you're gonna live in a rotating facility you might as well have stayed up in orbit in the O'Neill stations with all the old people.

>>10051748
I'm sure you still could for several hours a day, I merely envision it as a measure to facilitate permanent inhabitation of an object. This way you could live on the ring, maybe even work outside of it for a 40 hour week, and stay on the object indefinitely. The only alternative I see is having an orbiting rotating space station and a ground crew living in permanent lowered gravity that gets swapped out every couple of months.

>>10051753
Oh ok that would work. Carry on with your plan.

>>10051754
Or maybe not, you'd need some really big fucking ball bearings for a rotating ring on an astronomical object.

Why doesn't the latex work for me?
I whitelisted cdnjs.cloudflare and cdn.mathjax in umatrix...

>>10051801
You use /math the first time and /math the other times?

>>10051816
it's just a screencap from earlier in this thread.
e.g. [pic] is what I see for >>10049368

>>10051801
Temporarily disable umatrix or/and ublock and see what happens
If it doesn't work, try without extensions at all

>>10051827
You're right, it's ublock origin (alone).
I'll try to find a filter.
Thanks!

>>10051801
[math]testing^{done}[/math]

>>10051844
add:
@@||4chan.org^$csp

would it be possible to make a mug with thermonuclear heater to heat your coffe and enough shielding to not give you deadly radiation poisoning while drinking it?

Why does everyone in /sci/ seem to be against denying free will? Every time I see a thread of someone denying free will everyone else just calls him an idiot. I thought that the most predominant opinion in science was that free will didn't exist and the brain is just a complex organ that responds to external stimuli deterministically.

>>10051986
>I thought that the most predominant opinion in science was that free will didn't exist

Don't confuse science with r/atheism, faggot.

>>10051986
Because it only doesn't exist if you define free will as the ability to defy physics, which is basically saying "I can't flap my arms to fly, therefor I have no free will". You're still making decisions, regardless, and aren't omniscient, so you experience that process as free will. It may ultimately be an illusion, but science currently has no explanation for that illusion. It's never enough to simply label something illusion, you also need an explanation for the mechanism.

It's a core flaw in the old determinism debate, which really doesn't belong on >>>/sci/, as it's not that "science's opinion is that there's no free will", it's that, *most* accepted models of the universe support determinism - which only precludes free will under that ludicrous definition. Quantum woo be damned, you're still block universe until you have quantum gravity - but even there, some variants of said theory in progress support free will while others don't. Thus, the whole topic remains in the fuzzy realm of philosophy, as it isn't falsifiable.

https://plus.maths.org/content/why-block-time

>>10043290
By that logic you are retarded and therefore a woman. There's "education" on that graph

>>10052030
but math teachers need to have taken math, and for whatever reason, retards wanna teach math

>>10042531
What's the best place to learn latex?

I don't understand c and d.

>>10051700
This boils down to showing the graphs of 4y-1 and -sin(πy) intersect at only one point. Notice that the slope of the first graph is 4, while the slope of the second is always between -π and π. So if they ever do meet at a point (which you have shown they have), the first graph will race off and the second can never catch up with it - to do so it would need to be steeper than the first graph at some point. Fill in the details as needed to get the appropriate level of rigour.

>>10051719
i didn't think about it at all but have you tried starting with the assumption that it crosses the y axis twice? i.e. there exist 2 separate points of intersection

>>10052085
>I don't understand c and d.
What have you tried?

>>10051986
Because /sci/ as been invaded by incels and nihilists who want to blame their life on muh determinism.

>>10051986
>Why does everyone in /sci/ seem to be against denying free will?
Free will is a spectrum, and most of the people on /sci/ are born with little to no free will. Us on the other end of the spectrum have the privilege of enjoying life with free will.

>>10051986
Because free will obviously exists. /sci/ has been invaded by incels and nihilists who want to blame their life on muh determinism.

>>10052072
sticky

>>10051055
W is the set of all real valued functions on the interval [a, b] of which the function value at 6 is 10.

Whether or not W is a subspace of V depends on the operators which are defined on V.

For W to be a subspace of V the following has to hold:
>a) the zero vector, i.e. the constant function f=0 has to be included in W
>b) W has to be closed under both operators i.e. addition and scalar multiplication

neither a) nor b) holds in your case therefore it's not a subspace

this is all assuming pic related

>>10052417
>Something that defies all laws of nature and presupposes the existance of immaterial things obviously exists

>>10052497
What defies all laws of nature?

>>10052497
>presupposes the existance of immaterial things
we already know immaterial things exist tho
Like numbers, emotions, partial differential operators, etc.

>>10052535
Yeah sorry, I mean immaterial things that can act on the material world. When people say that we have free will and thus we can "decide", what is the thing that "decides", if not a brain that simply responds to external stimuli and is therefore deterministic?

Studying manifolds, in particular, constructing submanifolds of R^n. This theorem gives sufficient conditions to construct a submanifold. How on earth does this result work intuitively?

>>10052634
Why do you assume that free will and determinism are incompatible? Prove that "my brain responds only to physical stimuli" is contradictory to "I have free will."

Is global warming real?

>>10052725
You're basically looking at the equivalent of n dimensional level sets. Try it for polynomials in 2-3 variables to convince yourself.

>>10052725
If a + v is a point near a, then f(a + v) is approximately f(a) + Dv (where D is the derivative of f at a). So if you move infinitesimally along a v such that Dv is 0, then f stays constant. As D is surjective, its rank is m and so its nullity is n. That means you have n degrees of freedom to choose a v so that Dv = 0, which is the same as saying that there are n "directions" along which you can move so that you stay in the level set.

>>10052895
In the US, depends on your political affiliation. Everywhere else, yes.

>>10052497
>defies all laws of nature
Prove that there are laws of nature.
Prove that if there are laws of nature, that we know any of them.
Prove that from the laws we know, we have enough to arrive to that conclusion.

>>10052634
>I mean immaterial things that can act on the material world

Why not? There's nondata things that can act on the digital world.

>>10052895
>Is global warming real?
It's real in the minds of leftists.

>>10052895
Read a book and find out.

Do radioactive isotopes being in a compound with other elements change anything about their radioactivity?

Do you guys think its really worth it to double major in CS and Math? My main goal is to find employment directly after graduation and get paid well so I can start getting my life on track, maybe grad school after working for X years. But at the same time, not studying Math makes me feel like I'm "dumbing" myself down. I suppose a Math minor would split the difference

I'm liking Calc but it just seems like fancy plug-n-chug. not really sure what I'd think of late undergrad.

what the fuck
this is 1/600 right? 600 people have the genome, and so if you pick any one of those randomly it's gonna be a 1/600 chance they're the murderer.
doesn't matter that he was tested first or last or any order, just that he's part of the 600

I mean is that right? it obviously seems way too straightforward. probability is confusing, things are actually not simple when you think they are, i.e monty hall. I fucking hate this class.
I mean, we don't know P(someone is the murderer). of course, it's not 1/1000, I don't think I'm having conceptual issues. but I mean P(someone is the murderer | has genome) has to be 1/600, and P(has genome | is murderer) has to be 1.

>>10042531
>[math]\frac{\partial}{\partial t}[/math]

Anyone know how to do this with excel?

>>10053145
P(someone is the murderer | jew blood) = P(someone is the murderer & jew blood) / P(jew blood) = P(jew blood | someone is the murderer) * P(someone is the murderer) / P(jew blood)

murder has jew blood -> P(jew blood | someone is the murderer) = 1

P(someone is the murderer | jew blood) = P(someone is the murderer) / P(jew blood) = 1/1000 / 600/1000 = 1/600

>>10052400
c) alpha = (1 USN/hr)*(5 hours)
using the formula for the poisson distribution,
P[Y=2] = e^-5 *5^2 / 2!
d) I'm stumped

>>10042531
I have recently read about Fission Fragment drives, specifically their nano-fragments variants, and found that they are amazing but lack power. I am unable to find any source that explains why more thrust can't be extracted from them, so I decided to just study enough to figure out how you could increase the thrust using only the fission fragments.

Thing is, I have no idea where to even begin to be able to figure that out. I have college level physics and physics under my belt, but nothing more complex than that. Where do I start?

I keep getting the angular velocity as 1 rad/s and I know that's not correct.

>>10043432
Fuck yeah i do

>>10053329
It's 24/25 = 0.96 rad/s.

d/dt atan(u) = (du/dt)*(d/du atan(u)) = (du/dt)/(u^2+1)
d/dt (y/x) = (x.dy/dt-y.dx/dt)/x^2
=> d/dt atan(y/x) = (x.dy/dt-y.dx/dt)/x^2/((y/x)^2+1)
= (x.dy/dt-y.dx/dt)/(x^2+y^2)

x=150-60=90
y=165-45=120
dx/dt=-2*45=-90
dy/dt=2*60=120
=> d/dt atan(y/x) = (90*120-120*-90)/(90^2+120^2)
= 10800*2/(8100+14400)
= 21600/22500
= 24/25

>>10042531
Why don't they teach dimensions of distance to children in public school? Beyond saying that "time is the 4th dimension", which is very vague and ends up confusing a lot of people, they never say anything on it. So few people I have met are actually able to grasp that the dimensions are degrees of removal of a certain set of physical data.

How am I supposed to know the chemical formula for silver sulfide, excluding memorization of it? Writing out the electron configuration does not seem to help.

(The sulfide part has a charge of minus 2.)

>>10053450
data of high dimensionality is of no concern to a dramatically high percentile of people.
Kids tend to learn visually. How can you teach a child something that you can't visualize to them?
On the other hand, adults can easily understand dimensionality when you place it in the perspective of another parameter to an equation

>>10053484
Silver has a charge of 1+. Obviously, you'd need 2 Ag atoms to balance out the -2 of Sulfide

>>10053551
But how did you know that silver has that charge? Other then looking at reference material which is not the period table how do I figure this out? Writing out the electron configuration does not really help.

I guess I just have to memorize that silver has a 1+ charge, zinc and cadmium have a 2+ charge, copper is 1+ or 2+, and iron is 2+ or 3+.

>>10053569
"Since there are many exceptions to the formula, it would be better just to memorize the oxidation states for the fourth period transition metals, since they are more commonly used." --https://chem.libretexts.org/Textbook_Maps/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/3_d-Block_Elements/1b_Properties_of_Transition_Metals/Electron_Configuration_of_Transition_Metals/Oxidation_States_of_Transition_Metals

>>10053580
Fucking gay, I don't want to memorize shit.

>>10053592
Sort of helpful:
https://www.youtube.com/watch?v=E3Ok1qaXK_g
https://www.youtube.com/watch?v=0FPYIB9_fPY

>>10042531
If I were to be that astronaut and just push myself off the station towards Earth, how would I die?

Would I be roasted alive inside the suit?

How long would it take? Would the experience be worth it?

>>10042531
I’m new didn’t know these threads existed

Please read my stupid question here >>10053838

Humanities brainlet who never did math in high school at it again. This time I'm stuck on logarithms.
How do I solve (3log 2 - log 24):(log 3 + log 27)?

>>10053866
>how would I die?
You'd starve in space

My course started dumping a bunch of physical equations on me that I don't understand intuitively

Can anyone explain how the fuck the reaction-diffusion equation makes sense? I should be able to derive it somehow

why does hair on human heads keep growing instead of reaching constant size like hair on other body regions?

>>10053894

Numerator: 3log2 - log24 = log8 - log24 = log(8/24) = log(1/3)
Denominator: log3 + log27 = log(3*27) = log(81)
So the fraction ends up being log(1/3):log(81)

Which can be written as log81(1/3) i.e. log of 1/3 to base 81
This is the power to which 81 must be raised to reach 1/3
Luckily, it's kinda obvious that 81 is 9^2 = 3^4.
3^4 = 81 -> 3 = 81^(1/4) -> 1/3 = 81^(-1/4)
Answer is -1/4

>>10053919
What is reading comprehension, you stupid shit?

>>10046508
*tips fedora*

Why can't Mathematica derivate?

find the voltage across the capacitor as a function of time
q(0)=0

>>10054041
What is orbital mechanics, you stupid shit?

Can someone help me out with this? Or maybe if you have some similar examples you can share? I'm confused on how to setup the limits of integration.

>>10054097
But I'd eventually crash and burn in the atmosphere anyway, since I have, however weak, an acceleration towards Earth, right?

>>10054063
It's just 'D' for a derivative, and you also need to supply the function argument(s).

for example:
D[1/2 Cos[2 x ], x]

>>10054108
>But I'd eventually crash and burn in the atmosphere anyway
Only if you can jump REALLY hard. Jumping radially inwards will lower your orbit 90° ahead of your current position and raise it 90° before. But it's a pretty ineffective way to deorbit.
Jumping off retrograde requires less energy, but I don't think it's possible for a human either

>>10054098
[math]\int_{x=-1}^{x=0} \int_{y=-1}^{y=0} xy ~ dy ~dx = \int_{x=-1}^{x=0} \frac{xy^2}{2} |_{y=-1}^{y=0} ~dx = \frac{x^2 y^2}{4} |_{y=-1}^{y=0} |_{x=-1}^{x=0} = \frac{1}{4}[/math]

[math]\frac{4}{\pi} \int_{x=-1}^{x=0} \int_{y=-\sqrt{1-x^2}}^{y=0} xy ~ dy ~dx =~ ... [/math]

>>10054148
i got the first integral. However, where does the pi/4 come from and how do you know that the limits of x are -1 and 0?

average is 1/area * integral

Can someone explain me this relation dm/dx=v and dv/dx=W?

Why are moment and shear related? Is it through external forces that are applied on the beam?

>>10054184
Equilibrium of forces/moments

>>10042531
not a physicist but curious

when I have particles aligned along an electric field, does the size matter? will they align less if the particles get smaller?

How do I avoid stupid errors in math? I always do the calculations correctly in my head but on paper I always make some kind of foolish mistake.

>>10054063
Read the fucking documentation

How does the zero sum universe theory hold up to the fact the universe is expanding faster than light

>>10053879
I'm going to give you the benefit of the doubt and assume you're also new enough not to be aware of >>>/x/.

>>10054575
In a flat universe, that would be as expected.

>>10054335
Can you elaborate? sorry but im a brainlet

>>10042531
dis nigga got a bigger brain than most black people

>>10054073
V*R2/(R1+R2) (1-e^t/T)

Please help.
Need help with recursion relations.
I have no idea how to do them. My professor did not explain them very well during lecture. He gave us a handout but the problems it shows skip a lot of steps.

T(n) = 2T(n-1) + 2n. T(1) = 1.
I got the first 5 of it being 1, 6, 18, 44, and 98.
It's finding the closed form (where you can enter whatever number and it will give you the answer without needing the previous steps) that I am stuck on.
After expanding it a few times I got 2^4 * T(n-4) + 2^4 * (n-3) + 2^3 * (n-2) + 2^2 * (n-1) + 2n

After that, I'm not really sure where to go. I feel like if I could really understand this one I could do the others. It sucks because I have a test (in another class) the day before this homework is due, and it's due on Wednesday. So I want to get it done as soon as I can to study more for the test.

>>10054810
Fucking retarded cs majors...

[math]2^{N-1}+\sum_{i=2}^{i=N} i*2^{N-i+1} = 7*2^{N-1}-2N-4[/math]

>>10042531
If the light coming off the sun only hits half of the earth how are there pictures of the entire planet with light hitting all of it? s it a picture of that half? Forgive my autism.

>>10054901
the moon experiences phases of earth in the same way that the earth experiences phases of the moon, however the phases of earth will be opposite of the phases of the moon. When the moon is full, earth is new etc.

>>10054861
That doesn't answer the "how"
I didn't want the answer. I wanted to know how to get to it.

pls explain: my answer was 9807*(surface area of the quarter cylinder) *6m, but that's wrong.

How do I build a covariance matrix?
I want to calculate a chi square

[math] \chi^2 = \Delta^TC^{-1}\Delta [/math]

I have 100 events, for each I have observed three different variables, x, y and z to calculate the final value. My model is simple but for even more simplicity let's just say that

[math] x+y+z = A_{obs} [/math]

And I have a model that gives me [math] A_{theoretical} [/math]

so [math] \Delta = A_{theoretical} - A_{obs} [/math]

But how do I construct this covariance matrix C?
For x, y and z I have 100 points of data each, and each with a value of uncertainty as well.

tl:dr

how do I construct 100x100 covariance matrix out of 300 points of data and 300 points of uncertainties?

I didn't want to make a thread for this and I don't even want to bother the actual threads, but do you guys have to deal with conspiracy theory goofballs often? Flat Earth, NASA is faking their videos, maybe even a bit of back and forth with how authentic Global Warming is, ect.

>>10054625
For example
[math]V(x) - w(x) \Delta x - (V(x) + \Delta V) = 0[math]
Rearrange a bit
[math]\frac{\Delta V}{\Delta x} = -w(x)[math]
You can write Delta V as V(x + h) - V(x) and Delta x as h. Take the limit as h approaches 0 and you have the definition of the derivative dV/dx

>>10055066
You must be new here... Check the catalog - that's all we deal with. (Granted, most of them are trolls.)

>>10054951
This is what you get for failing calculus
[math]\sum_0^N x^n = (1-x^{N+1})/1-x [/math]
take derivative
multiply by x
let x=1/2
multiply by 2^N+1

I don't understand this problem. According to chegg the capacitor charges on the positive half cycle and discharges on the negative half cycle. Isn't the capacitor constantly being charged? I would greatly appreciate help or any advice in the right direction. I am absolutely lost by chegg's method.

>>10055227
Sorry, discharges on positive and charges on negative cycle.

>>10055227
Let C be discharged
When V1 is -10V, C as measured by Vc=V0-V1 charges up to 10V so that V0 = 0V
When V1 switches to 10V, V0 = V1+Vc = 10V+10V = 20V and start dropping back to 0V
etc

>>10054810
T(n) = 2T(n-1) + 2n
=> T(n)-T(n-1) = T(n-1) + 2n
By analogy with differential equations, the T(n-1) on the RHS means that T(n) has an exponential component. The 2n means that T(n) has a quadratic component.

For the exponential component, T(n)=2*T(n-1)=>T(n)=k*2^n.

For the quadratic component, set T(n)=a*n^2+b*n+c.
T(n)=2*T(n-1)+2*n
=> a*n^2+b*n+c = 2*(a*(n-1)^2+b*(n-1)+c)+2*n
=> a*n^2 + (-4a+b+2)*n + (2a-2b+c) = 0
=> a=0, -4a+b+2=0, 2a-2b+c=0
=> a=0, b=-2, c=-4

T(n) = k*2^n - 2*n - 4
T(1) = 2*k-6
T(1) = 1 => 2k-6=1 => 2k=7 => k=7/2

T(n) = (7/2)*2^n - 2*n - 4

>>10055245
This is the answer which is why I am so confused.

>>10055257
Oh, wow. That is vastly different than the way my professor tried to show us in class. From what I could tell, he tried to show us by expanding it like I did in my OP, then finding what's changing and using (I believe) geometric summation.
I've never seen it solved the way you just did it, but it looks a lot more straightforward than however my professor was trying to show us. Thanks.
Really wish there were more youtube videos of these sort of problems since I learn a lot better from watching examples. There was plenty of them for math questions and it really helped me in calc. But I just can't seem to find very many about this kind of stuff.

how do you deal with procrastination bros

Hey, guys. Need some help deciding between majoring in pharmaceutical sciences or biotech.

I recently asked a professor to write me a letter of recommendation for graduate school and he told me to write it and he would change the pronouns and put his name on it.

Is this enough of a red flag that I should try to find somebody else, or should I just go with it? I don't know if this is a common thing that people just hush over or if it's as sketchy as it feels to me.

>>10055531
Literally just do it. Thinking about ways to overcome procrastination is just more procrastination.

>>10055282
So CR>>>T so it never gets to fall to 0
At the steady state, charge in in one half cycle equals the charge out in the other cycle.
>(Vop)T/2R + (Von)T/R = 0
>0 = Vop+2*Von

Since C isn't changing voltage, the peak to peak is still the same.
>20V = Vop - Von
>-20/3 V = Von
>40/3 V = Vop

>>10050253
False, they use your skin color to decide that

I'm working on some computer science homework one of the problems is to Dijkstra's algorithm to find the shortest path from vertex 5 to all other nodes from this adjacency matrix. But wouldn't the shortest path from 5 to all the other vertices be a direct path?

>>10055869
dont forget vaginas

How do I solve for a variable in a equation that has partial derivatives???

>>10056159
See if it has one of the forms given in
en.wikipedia.org/wiki/Partial_differential_equation#Analytical_solutions
Otherwise you're stuck with a numerical solution (e.g. finite element method).

>>10055873
For that particular graph, yes. You can confirm that without using Dijkstra's method (or similar) from the fact that the highest value is less than twice the lowest (excluding zero), so any indirect route must be longer than the direct route.

But that isn't always the case. Even if there's a direct route to every other node, the direct route isn't necessarily the shortest path.

>>10055575
If he doesn't approve of what you're writing, then he won't sign it, so don't overexaggerate. You should have at least 2-3 letters anyways so just go with it if you can't find anybody else.

Also nice way of saying you're a girl, so show your tits

>>10055042
I want to do it as described here
https://www-cdf.fnal.gov/physics/statistics/notes/cdf8661_chi2fit_w_corr_syst.pdf
but i don't understand how to apply my data on this

How do I represent C5H12O2 only with sigma bonds? Do I put them whichever way?

how do I stop getting lost in the algebra when I'm doing calculus?

>>10057121
Calculus is where you finally learn to stop messing up algebra.

>>10057124
I noticed that much, the chain rule and implicit differentiation are kicking my ass because of it

Alright I have a dataset with scores from 0 to 800 which I map to a score 0 to 10 through y=×/80. However the data set is skewed towards low values, kind of a pareto (not sure if right word) distribution.
How do I change my formula to get a more "linear" scoring result?

>>10042531
Can using a website like 4chan for long periods of time, affect your epigenetics?

>>10057434
I worded that shit wrong. fuuuck

what's the best undergrad stem major for landing a job right after college?

>>10057330
Just calculate the percentiles

ANY DECENT 3D GRAPHIC CALCULATOR? NOT GEOGEBRA SHIT??

>>10056244
Thanks anon, I was a little supicous because it looked to easy to be true.

Approximate the maximum possible percent error in measuring the volume of a right circular cylinder given the possivle errors are 5% and 3% for the radius and height respectively.
My work is in the picture.
So how do I eliminate the unknowns? Don’t I need them to solve this?

>>10057867

>>10057867
>>10057875
The Radius r and height h of a right circular cylinder are measured with possible errors of 5% and 3% respectively. Approximate the maximum possible percent error in measuring the volume.

dr = .05
dh = .03
V = pi*r^2*h
Here I took the partial of V with respect to r times dr + partial of V with respect to h times dh
dV = 2pi*r*dr + pi*r^2*dh

dV/V = 2/r * dr + 1/h * dh

What do I do now? There are no values of R or H to work with. Any ideas?

I'm in discrete math. How do I solve "if a and b are rational numbers, then a^b is rational" using a direct proof?

#!/bin/bash
while ! foo
do
sleep 1
echo "Restarting program..."
done

Why does the above script open foo in the first place? How does it start foo again if it fails? Shouldn't it just check if foo is not running and echo a message?

>>10058427
What have you tried? you're probably overthinking it

>>10058427
> if a and b are rational numbers, then a^b is rational
That statement isn't true in general. E.g. a=2, b=1/2, a^b=sqrt(2) which is irrational.

>>10058484
I'm having trouble because I have to disprove it using a direct proof and not a proof by cases. All I've got is setting a equal to x/y where y is not 0 and b to p/q where q is not 0. If I do it this way, I somehow have to come to the conclusion that x/y^p/q is or is not rational.

>>10058577
just look up the proof that sqrt(2) is irrational and use that method

>>10058577
(x/y)^(p/q)=a/b
=> (x/y)^p=(a/b)^q
=> x^p/y^p=a^q/b^q
=> x^p*b^q=y^p*a^q
If that equation has an integer solution, then (x/y)^(p/q) is rational, otherwise it isn't.

If you break down x and y into prime factors, the factorisations of x^p, y^p and (x/y)^p have exponents which are multiples of p. Similarly, the factorisations of a^q, b^q and (a/b)^q will have exponents which are multiples of q. So in order for (x/y)^p=(a/b)^q to have a solution, for each prime factor of (x/y)^p the exponent must be a multiple of q.

Without loss of generality, we can assume that x and y are coprime, as are p and q. I.e. their prime factorisations will have no primes in common. So the prime factors of (x/y)^p will have exponents which are a multiple of p. In order for these exponents to also be multiples of q, x and y must have the form x'^q and y'^q respectively, i.e. both numerator and denominator must be perfect squares/cubes/whatever-^q-is.