/sqt/ - Stupid Questions Thread

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i don't get it. something about nice guys/friend zone?

>>8929302
She'll get "put out" by the bad boy.

Continued from last thread.
Where does the arcsin come from when you integrate sqrt(25=x^2)?
Is there an easy way to explain how to do this?
-t. calc 2 brainlet.

>>8929316

http://www.integral-calculator.com/
http://www.derivative-calculator.net/

>>8929316
Short answer: trig
Long answer: read a trig book
Medium answer: Just try to integrate eith that technique. The trigonometric functions have a nice property that allows you to turn a complex integral (complex=not possible to evaluate) into a simple integral (possible to evaluate). What those properties are will be apparent from the moment you try do trig sub. It is literally the entire point of trig sub.

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>>8929337
>>8929333
>Professor gives out this problem on weekly test
>We haven't gone over trig sub yet
This is going to be a fun semester.

>>8929342
if you know basic trig functions like sin^2(x)+cos^2(x)=1, half/double angle formula, tan^2(x)+1=sec^2(x) you will be okay for trig substitution.

>>8929342
Well, trig sub is just the fancy name given to the general and completely developed technique. If you know trig you can figure out the simple special cases to integrate that. You can easily "discover" trig sub because it is simply sin^2 + cos^2 = 1

Is there a place for calc review problems? Like calc1-4?

I don't understand u-substitution for integrals.
Why do we treat the [math]\frac{du}{dx}[/math] as an arithmetic fraction and perform algebra on it?
I don't even really understand what the [math]\frac{d}{dx}[/math] or the [math]dx[/math] at the end of an integral _really_ means, no one ever explained it.

>>8929639
It's just a rule of thumb to make the computation easy, but it's in no way something you should take as a rigorous mathematical statement. If you want a proof, try googling it.

>>8929639
>Why do we treat the dudx as an arithmetic fraction and perform algebra on it?
i have really struggled with whether and how to respond to this. The execution of this message was very nice and respectful, and I genuinely appreciate that. The premise, however, is problematic. Maybe not inherently, but within the context of the sexist society we live in. Men are allowed, and often feel compelled, to think out loud at women, to share unsolicited not necessarily informed thoughts at women. (And usually these men, unlike you, don’t even seem to recognize that their thoughts may not be useful.) Women on the other hand aren’t allowed to be as open. So, if you want to not just be respectful, but actually be anti-oppression, it is better (IMO) not to respond to a woman’s work with the types of thoughts that other men pawn off as insights, if you know what i mean. again, i appreciate your honesty, but i feel obligated to point these things out.

>tfw too fucking dumb to understand trig substitution

Does anyone have a resource, video, etc that breaks this down in absolute brainlet terms? When I look at examples I literally have no clue where the substitution function comes from or how you determine it. I dropped Calc II last semester after getting lost in it and have to pass it this summer.

>>8929316
Another calc 2 brainlet here.

I've gotten as far as converting this equation into the integral of cos^2x.

What is the integral of cos^2x?

>>8929766
Okay google helped me.
How are you supposed to remember every trig identity?

>>8929771
>How are you supposed to remember every trig identity?
you're not

>>8929766
Wolfram it. It's ugly.

>>8929395
I second this question.

>>8929773
My calc II proof expects us to. He has shitty problems where you trig sub using double/half angle formulas including obscure af ones for cofunctions.

>>8929774
Wolfram engine must have fucked up because once you convert it to 1/2*(1+cos(2x)) it's pretty simple.

Seriously I don't trust any ugly answer that comes out of wolfram, chances are the algorithm just failed for what you gave it.

Why are the rationals countable? I know there's a proof using Cantor, but I don't know enough math to understand Cantor's stuff yet. According to Wikipedia, a set is uncountable if it's cardinality exceeds the set of natural numbers, but doesn't the cardinality of rationals exceed the set of N?

I mean you can go 1/1, 1/2, 1/3, etc all the way to infinity, and do that with every integer as the numerator as well. It looks uncountable to me.

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>>8929812

>>8929816
So why can't you draw diagrams like that with irrationals? Even if they go on forever, some are larger than others, and can, in theory, be ordered.

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>>8929819

>>8929819
because given any list of irrationals you can construct a new one not on that list

Can anyone recommend a textbook for quantum physics? Something suitable for self-teaching, preferably.

>>8929864
First, do you know the math? Second, shankar.

>>8929766
Linearize it first with double angle identity.
cos^2x=(cos2x+1)/2

Damn, posted this in the old thread without noticing there was a new one:

Thinking about majoring in chemical engineering but heard its incredibly hard to find work.

Are the job prospects really that bad? Any chemical engineer here struggle to find work? I live in California so it feels like my options for employment are heavily limited.

\frac{d}{dx} [e^{\int p(x) \, dx}]

How this works

>>8929902
kek
[math]\frac{d}{dx} [e^{\int p(x) \, dx}][/math]

>>8929904
>>8929902
Dw I figured it out

>>8929904
p(x)e^int(p(x))dx
Derivative of e^f(x) is f'(x)e^f(x), derivative of int(p(x))dx is p(x).

I think I'm missing something regarding complexity theory. Can someone answer the following (preferably with examples):

>Are there problems that are in NP that aren't NP-complete and aren't in P?
>Why aren't all problems in EXPTIME NP-hard if NP is in EXPTIME?
>Why is the halting problem NP-hard? Surely since NP refers to all decision problems then that implies that anything that's NP-hard is decidable?
>How do we know that NP-hard problems like SAT are the hardest problems in NP? Could we potentially find a harder problem than SAT that's still in NP?

Looking to major in applied math in college and minor in Chem. Am I wasting my time? Should I just do actuarial maths and make the big bucks? Or do I have a shot at moolah with my current choice of degree? Save the "do what you want" lecture, I'm fucking broke and strictly just looking for the math based major that will gimme the best payout. Comp sci is not an option. Applied math vs. actuary maths. Go!!!

>had anyone used NetLogo
>does anyone use NetLogo

>>8930082
Economics is pretty math based.

>>8929819

Are you familiar with one-to-one and onto functions?

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I feel like this is something really obvious but I'm an algebralet and I'm not sure specifically what terms to search for. How does he get x^2 −2x−2=0 from x^2 −2x−2=0 / (x^2 +2)^2 ?

What am I supposed to do in cases like that?

>>8930144
Multiply both sides of the equation by the denominator

>>8930150
If I multiply the left side by zero, it stays zero, right?

>>8930159
Yes, anything multiplied by 0 is 0. Think about it like this, you want to find when that equation equals 0 you know that 0 divided by anything is 0 like 0/6 = 0 so you just need to find out when the numerator is 0, thats when the entire left side of that equation is 0.

>>8930082
>I'm fucking broke and strictly just looking for the math based major that will gimme the best payout.

Look at entry level job posting and see what courses they want to see.

>>8930162
Ok, but could you show how multiplying by the denominator yields x^2 -2x -2 = 0?

I'm getting something wildly different.

>>8930169
How can you get something wildly different? What are you getting?

>>8930082
major in applied math and minor in comp sci faggot

>>8930183
Well (x^2 + 2)^2 is x^4 + 4x^2 + 4, so multiplying that against the numerator is going to give a polynomial starting with X^5. Nothing close to the answer.

>>8930191
x^6 rather

>>8930191
But isn't (x^2 + 2)^2 also in the denominator? So it would cancel out on that side.

>>8930193
I don't see it in the numerator

>>8930197
>But isn't (x^2 + 2)^2 also in the denominator?
>I don't see it in the numerator

>>8930199
>also

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>>8930197

>>8930202
Hey, you're the one who doesn't get that a/b = 0 implies a = 0.

>>8930203
Ok, but how does x^2 become positive and 2x become negative?

>>8930205
and +2 become -2 as well

>>8930205
You can multiply both side by -1

>>8930205
(-x^2 + 2x + 2)*(-1) = ?

>>8930208
That makes sense, but why would I do that specifically? Does it make factoring the polynomial easier?

>>8930210
x^2 - 2x -2

>>8930212
Yes and its also a convention to not have leading terms be negative

>>8930215
Ok, thank you.

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I need a biologyfag to help me out here.
Every time I wake up from sleep, no matter if it was a one hour nap or a ten hour rest, no matter if I fell asleep tired or not, no matter any variables at all, I always awake in a state of delirium and what I'd describe as temporary amnesia. This didn't start happening until a couple weeks ago. I'll try to describe to the best of my ability; I wake up confused about where I am, thinking nonsensical thoughts (i.e, today I woke up terrified of my pillow, thinking something about green crystals, and the day before about stuffed animal tulpas.) I know how 'xd random' that sounds, I am not making a joke- these 'episodes' can last for well over ten minutes and I had the cops called to my apartment before because I was literally screaming at the top of my lungs for a solid five to ten minutes. Is this a documented thing? I realize this sounds like a retarded joke but it's not and I am legitimately worried that I might have some degenerative brain disease or something. Other sleep related problems include that I usually wake up feeling like blood is rushing to my head (I sleep with my head on a pillow, not leaning down or anything though) and sometimes I can't see anything besides solid white for up to thirty seconds after waking up. I should probably mention that I can remember these fits clearly, it's not a muddled memory or anything. No changes in my lifestyle either that could trigger this either.

>>8929639
>>8924263

>>8930232
It may have something to do with your blood pressure affecting your brain's oxygenation while you sleep, giving you mild hypoxia when you awake, which would absolutely throw you into a delirium. I'm not a biologyfag, but I've suffered from blood-pressure related hypoxia before and sometimes get very mild versions of what you describe.

It sounds quite serious, anon. I think you should see a doctor. If what I'm saying has any truth to it though, you can at least rest assured that your brain is not degenerating, just starved for oxygen.

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>>8929294

Why are the Fraunhofer lines of heavy elements (Calcium, Sodium...) more prominent than those of Hydrogen and Helium in the solar spectrum? There are way more lighter elements so why don't they have a greater effect on the spectrum?

do terrorist attacks follow a poisson process?

>>8929294
so i get

delta enthalpy of reaction = -21 kj/mol
delta gibbs e of reaction = -8.2 kj/mol

both i calculated correctly

for delta entropy of reaction i get = -35 j/(k*mol)

which was correct, until the prof changed the sign on the grounds of "entropy cant ever be negative", so she just changed it to +35 j/(k*mol)

is her reasoning correct? actually it was a classmate who told her

delta G = delta H - T delta S

can you just switch signs on delta S like that?

>>8930232
try sleeping with a pillow under your feet, elevating them

>>8930350
In what way? By location or time?
Either way I doubt it, since terrorist organisations probably want to spread them out to make them as unpredictable as possible.

>>8930350

I assume as a time process.

Run the data, see what the MLE gives you as a parameter and evaluate the fit with an F-test

>>8930419
>>8930350
>that data would not be terribley hard to find
>it'd probably neEd to be transformed

>If you have 2n points arbitrarily placed in [math]\Re^3[/math], what is the maximum number of connections between the points an arbitrarily placed plane can 'cut'?
I have no fucking clue how to do this, i've tried all the geometry I can, do I need to use multi-variable calculus? Am I a brainlet?

>>8930450
Good question, you should be able to formulate the situation that maximizes possible edges, now think about graphs.

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So, I took a [math]^{1}\text{H}[/math] NMR spectrum of pic related and I seem to get a weird [math]^{3,4}\text{J}[/math] coupling in both the ortho and the meta proton with the same coupling constant of 1.1 Hz. I know that this might be from a coupling with [math]^{15}\text{N}[/math] or [math]^{17}\text{O}[/math], but I'm not sure which one. Judging from the MS, the product does not have any impurities. Can anyone help me? I'd really appreciate it.

>>8930480
Nvm, got it. They couple with each other. Should've realised that earlier...

>>8930450
n^2

>>8930466
>you should be able to formulate the situation that maximizes possible edges
thats literally the question

>>8930530
how?

>>8929316
The answer given in the last thread is still there:
>>8929228

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>posts the wrong image
Oops. Again,

How would I attempt to prove this? I can understand how there's elements of order 2 and 7, but not sure on the last identity. I haven't done a course on group presentations, so can't use any possible theorems that make this rather simple.

>>8930981
i dont know what theorems you know but the group has to be D4

>>8930996
Heh, that's the next part of the question. I know the required isomorphism to show that but I guess I can't use it here since it's the answer to ii)

>>8930981
what did you use to show the existence of a,b with order 7 and 2?

>>8931014
I was going for using Lagrange's theorem, but now you mention it that doesn't mean that the group can't be a load of elements with order 2 and none of order 7..

>>8931052
yeah lagrange won't do it

do you know sylow theorems?

>>8931065
Oh. They were in this module last year but were moved to a different one this year. I assumed that this question didn't require them. Damn

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>>8929316

>>8929294
A quantity is measured by two different methods and the values and standard deviations are

x1 +σ 1 = 1.5 ±0.6 and x2 + σ2 = 2.9 ±1.5

The value of the test is : ?

What do I calculate with?

>>8931093
t= (|x1−x2|)/
(√(?x1)^2 +(?x2)^2)

>>8931069
It's a consequence of them.

Is the formula for triangle numbers used outside of discrete mathematics?

If I give my hormone therapy hormones to my cat will it turn into a cat girl

>>8931306
cant you just get a cat thats a girl and have sex with it?

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>>8929294
Currently learning about Laplace Transforms, and I'm a bit puzzled by an example...

Why would [math]\lim_{t \to \inf} \frac{-t}{s} e^{-st}[/math]
be zero?

>>8931384
try using the taylor series for the exponential function

>>8931385
Thank you very much!

I just got a bit confused because when I used L'Hopital's Rule, I got the derivative to be equal to:

[math]
-\frac{1}{s}e^{-st} + -t^2 e^{-st}
[/math]
Which I don't think brings me closer to the answer.

>>8931401
Might have dropped a negative somewhere accidentally

Is (A^-1)A necessarily equal to the identity matrix?

>>8931384
Because (e^-st) is equal to 1/(e^st), and if t is approaching infinity, the denominator will increase at a fuckhuge rate so the function will equal zero. If you don't believe me, do a l'hopital.

>>8931450
yes, that's how A^-1 is defined

Is there any point in living if we one day die and fade into a void of nothingness, as if nothing ever happened?

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>>8931455
I don't think that's right though, matrix multiplication is generally anticommutative.

>>8931461
yes but for finite dimensional matrices, a matrix is a left inverse if and only if it's a right inverse too

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>>8931466
Shit that makes sense with a test I took a few months back. Thanks bud.

>>8931461
>>8931466
>finite dimensional matrices, a matrix is a left inverse if and only if it's a right inverse too

[1, 0]*[1; 0] = [1]
[1;0]*[1,0] = [1, 0; 0, 0]

>>8931477
but those aren't square matrices

>>8931477
those are vectors, not matrices

>>8931486
It's a 2x1 matrix and a 1x2 matrix

>>8931481
Who said anything about squares

>>8931571
wat

I thought matrices have to be square to have an inverse by the IMT

>>8931486
>he thinks being pedantic will make him look smart

Which areas of math are most relevant to comp sci (yes, I know it's a meme major :[ )?

>>8931571
>It's a 2x1 matrix and a 1x2 matrix
doesn't exist as far as i'm concerned

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Did my lecturer fuck up on this slide? Learning about vectors.

>Angle of 30 degrees = [math]\frac{\pi}{3}[\math]
Cos

>>8931587
Disregard this, I get where [math]\frac{\pi}{3}[\math] came from now

>>8931587
Isn't 30 degrees from the x axis [math]\frac{\pi}{6}[\math]?

>>8931454
I tried L'Hopital, but through product rule, I get a weird term... (See >>8931401)
Am I deriving correctly?

(1/3)+(1/3)+(1/3)=/= 1 correct?

>>8931571
>Who said anything about squares
find me a definition of inverse matrix for non-square matrices then we'll talk

>>8931613
l'hopital is just the derivative of the top over the derivative of the bottom. I think you used it incorrectly. The numerator should become -1 , the denominator should become s^2(e^st). To me it looks like you differentiated the e incorrectly.

>>8931615
Fuck you're right... Thanks!!

>>8931585
Those are matrices, just not square ones

>>8931663
and what do they have to do with inverse matrices?

>>8931745
Nothing. Only square matrices can be inverted

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I don't understand this. Isn't this matrix an identity matrix, just a scaled one?

>>8931781
If U transpose was the inverse of U then it would equal the identity matrix exactly

How much force is required to increase the speed of 1 kg object from 5 to 10m/s?

>>8932004
not as much as your mom

>>8932004
It takes 37.5J of energy (0.5*m*(vf^2-vi^2)), how you apply that energy is up to you. If it's constant acceleration then you can use the time elapsed or distance travelled to figure out the force.

I will have my house fumigated with Vikane gas(sufuryl fluoride). Are my anime figures safe to leave as is? Do I need to take them out of the house?

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please.

what is the brainlet explaination for a function being bijective, injective, or surjective

>>8932275
injective: everything in the image of your function gets mapped to by exactly one element of the domain

surjective: every element in the range of your function gets mapped to by some element of the domain

bijective: injective and surjective

>>8929302
> Show that dot products are positive definite kernels
Are dot products positive definite kernels or positive semi-definite kernels?

>>8932290
dot products are positive definite, i don't know why you're calling it a kernel though

How do I learn math? Where do I learn math? I'm missing quite a lot of basics even, don't need to become proficient but I do need some levels above where I currently am and I can't seem to progress on my own with the sites I find.

is this relation on valid at failure, or can it be used with any stress and known fracture toughness to determine crack size?

Fracture toughness = Stress*sqrt(pi*half crack length)

does quantum uncertainty play any role in our brains?

What type of waves are all electromagnetic waves.

t shit at physics

>>8932273
i would guess that it's safe but if it's not too inconvenient i'd take them out to be sure

>>8932422
visible light
infrared light
ultraviolet light
x-rays
gamma rays
microwaves
radio waves

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Can someone explain to me why does x2(t) has the +6 component? Where does it come from?

>>8932549
not sure what i'm looking at here but i'm guessing it's so that (-2t + 6) is 0 at t=3

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>>8929294
Can someone pls explain how to answer question 29?

>>8932574
h / d = s / v

>>8932571

I think you're correct though, makes more sense to me now.

It's showing an example of how to construct a signal (ie the one on the graph) using step u(t) and ramp functions tu(t).

>>8932585
oh yeah and i think it's (-2t - 6) instead of (-t + 3) because the peak of x(t) is 2

>>8932584
Wut

>>8932610
similar triangles

the height of the flag divided by the total distance is equal to the height of the dotted line divided by the distance to his eyes

>>8932317
https://www.khanacademy.org/
>>8932337
No

Now for my stupid question:
>Prove that [math]\frac{2n-3}{3n+5}[/math] is irreducible for all integers [math]n > 1[/math]
I know the condition that you need the numerator and denominator to not have a common factor, but i'm stuck on where to go from there

>>8930357
Entropy can't be negative, but change in entropy can be, e.g. for freezing and condensation. She sounds retarded.

>>8932664
try the cases where n is even and odd.

>>8932725
I tried your way but didn't see how it helped, although I managed to solve it anyway, what did you mean by this?

>>8932664
High school brainlet here but try polynomial division

>>8932756
my bad, I did it in my head. For some reason I thought 3*2n was odd, which would've meant either the numerator was odd and denominator even or the other way around.

I just finished my physics course, and am moving into machine learning/statistics. I'm mostly interested in the most rigorous formulation possible. What textbooks would /sci/ recommend for someone who's not very comfortable with either discrete maths or statistics, but who wants it to be a bit harder than a usual undergrad introduction. To give you an idea the last thing I did for my course was differential geometry.

Thanks, hope the question isn't too vague

>>8932797

I tried on my own with polynomial division ( i get a rest of 19 ) and manage to solve the end wih cogruences equations but it feels to complicated, i think i'm missing a simpler way.

How do I get a girl to like me?

I'm supposed to implement some mathematical formula from a paper. it goes something like
[math] y_i - Cx_i^\theta [/math]
Now [math] y_i [/math] is defined, [math] x_i [/math] is defined, and [math] \theta [/math] is defined.
But C isn't even mentioned anywhere else. However, this is supposed to be a power law equation. What does the C mean in that context?

>>8932860
save up a lot of money

>>8932860
Just be yourself, anon.

>>8932860
>>>/soc/

>>8932884
doesn't work if you're autistic or an outcast because you don't have the years and years of natural training in social skills etc to be "yourself".

>>8932878
>>8932884
What formula is this?

>>8932853
>>8932820
I wrote the question wrong, the denominator is 3n - 5, heres my solution if you still care

Assume [math]\frac{2n-3}{3n-5}[/math] is reducible, i.e. [math]\exists k > 1[/math] such that [math]k|2n-3[/math] and [math]k|3n-5[/math]
[math]\implies 2n-3 \equiv 3n-5 \equiv 0 \pmod k[/math]
[math]\implies 6n-9 \equiv 6n - 10 \equiv 0 \pmod k[/math]
[math]\implies 1 \equiv 0 \pmod k \implies k = 1[/math]
Contradiction, therefore the fraction is irreducible

>>8932895
The cutie system of linear inequalities:
love = u + me
i <3 u

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Where do I start if I'm a brainlet?

>>8932928
>I wrote the question wrong, the denominator is 3n - 5, heres my solution if you still care
Oh that makes it much easier

I simplified the expression to 2/3 + 1/(9n-15) which is obviously irreducible

>>8932860
you're on the wrong website kiddo

>>8932943
i <3 u

i < 3u

Hey, what does the less/greater-then signs mean in the context of complex numbers?

>>8932943
i < 3 u?
i < 3 * u?
I am smaller than you, three times?
really made me think

>>8932976
Wow that is a lot easier, im really dumb
To be fair my proof was for if it was 3n + 5, then I looked back on the worksheet and saw I misread it and retrofitted it

>>8932973
Set theory

>>8932982
>>8932983
<3 is itself an equivilance relation on 2 people

>>8932973
Either Logic or Set Theory. Doesn't really matter which one. But set theory is normally recommended.

Do Graph Theory next, it is fun and easy to understand.

Definitely wait with Sequences and Series until after you do Set Theory, or you won't understand anything

>>8932982
>Hey, what does the less/greater-then signs mean in the context of complex numbers?
nothing, unless you consider absolute values

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Could someone guide me on doing this question? I can't find any example in Sipsters book (3rd edition) on how to "manually" solve something using rices theorem.

I'm assuming I just don't have to show that the property is not trivial then invoke Rices theorem, I actually have to construct a decider for this language and show that its the same thing as solving the halting problem which leads to a contradiction I think?

Im trying to finish up this assignment on alternating current circuits but am left with one question i cant figure out the answer to
Ive calculated capacitive reactance = 568.41 ohms at 50 Hz
and 27.07 ohms at 1050 Hz
but where to go from there i am just lost

Question as follows

Supply is 230V
A fluorescent lamp uses a 5.6µF PF improvement capacitor that takes excessive current when the 1050Hz signal is used for controlled load switching. What value of choke is needed to limit the current to the normal 50Hz value of 0.4A?

>>8933168
what book is this?

>>8933226
what do you mean what book? this is an assignment problem, but I was just referring to Michael Sipsters Intro to computability 3rd ed in the fact that there was no worked examples of "manually" solving rices theorem

>>8933235
ah I searched it but nothing came up. I think it's spelled sipser and google didn't pick up on it. Thanks anyway

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Do you think STEM will still be relevant 50 years from now. I mean, for the last 30 years or so whoever got a STEM field job is doing pretty well in life. Will this trend continue or will there be just an increasingly competitive market and "mainstreamnization" of STEM fields?

>>8933335
Well i don't want to bring politics into this, but refugees are invading our countries and bringing down the wages of working class jobs.
So your only options for a profitable job are either STEM or Law, Medicine or Business/Economy.

>>8932983
you're a big guy

So I'm trying to self educate myself on just about everything. I've been trying to watch documentaries on Quantum Mechanics and Relativity but they use a lot of concepts that I don't know. Stuff like thermodynamics, optics, kinetic energy and so on. So what do you guys recommend for me to study more before diving into other things. What principles should I understand if I want to have a good overall understanding of all of Physics. More importantly what path should I take? I'm thinking of bricks, what bricks do I need and in what order should I place those bricks in order to build this tower of Physics? I need directions.

>>8933487
>So I'm trying to self educate myself on just about everything.
is this guy serious?

>>8933571
What did I say was wrong?

>>8933487
https://www.youtube.com/channel/UCiEHVhv0SBMpP75JbzJShqw

watch all the lecture, do all the homework

https://cnx.org/contents/[email protected]:bG-_rWXy@5/Introduction

https://cnx.org/contents/[email protected]:DSrCtKWS@2/Introduction

https://cnx.org/contents/[email protected]:bq-wv5M8@3/Introduction

some good supplementary books should definitely read

You need a solid understanding of trig and Cal I before you can even think of starting with this shit, but there are plenty of available resources online to learn them. Physics will be hard and tedious to learn, if it isn't then you're doing it wrong

>>8933487
Learn high school physics
http://4chan-science.wikia.com/wiki/Physics_Textbook_Recommendations#High_School

Everything else is just higher order corrections.

If i'm trying to derive motion for an object in free fall with air resistance can I do:

F=mg-F_drag
ma=mg-1/2C_dApv^2
dv/dt=g-1/(2m)C_dApv^2

and then separate variables? I get something involving hyperbolic tangent and that doesnt really seem right.

>>8929294
Let's sew how smart you guys really are:
>>>17256245

>>8933670
>>>/o/17256245
Don't know why that did not work

>>8933672
>>/o/17256994
wew

Also since when did 4chan have post numbers for individual boards?

>>8933415
for you

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Newton seems very easy to understand.
When it comes to Einstein I have to squeeze my head but it still makes (some) sense.
Quantum physics is just completely insane and although I accept it as fact it seems as believable as /x/ threads.
Is this normal or am I just dumb?

>>8933819
since always, i think?

>>8933842
If you don't understand the math, you know jack shit popsci retard.

>>8933819
>>>/o/17256994
I'll just neck myself.

>>8933857
I was pretty sure that before moot sold out you could link to another board's post without having to add >/o/ in there at the very least.

>>8933879
And if you think Physics is just Math you're far worse as well.

>>8933890
Physics begins with math. After you are comfortable with the math, you can talk physics however you want. Spouting pop-sci bullshit isn't understanding because you literally don't know the actual language it's expressed in.

>>8933923
Anime begins with Japanese language. After you are comfortable with Japanese language, you can talk anime however you want. Spouting weeaboo bullshit isn't understanding because you literally don't know the actual language it's expressed in.

>>8933923
this

without the math it's just normie tier mental masturbation. you may as well read fiction instead.

>>8933939
Okey, so your little weeb mind can understand. Physics subs are horrible and there's substantial amount of stuff lost in translation.

>>8933963
I was just making a shitty joke. I guess "pop-sci" should be replaced with "subtitled" instead.

Are 2 summer REUs enough research to get into a top grad school (EE MS or PhD) ? I might be able to also do some research during senior but not certain given my university. My gpa is 3.97 and only worried about research desu. Looking at most top programs outside of California.

>>8932275
Its bijective if there's exactly one pigeon in each pigeon-hole, injective if there's no more than one pigeon in any pigeon-hole, and surjective if there's at least one pigeon in every pigeon-hole

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So I'm learning about vectors, and this question comes up. How is this plane defined by only one vector? Does this plane stretch to infinity in the direction perpendicular to the vector?

>>8934075
>How is this plane defined by only one vector?
it's not, the choice of a point (the origin) is important here

> Does this plane stretch to infinity in the direction perpendicular to the vector?
in _every_ direction perpendicular to the vector, relative to the origin

Is there a reason why limit needs to be written the way it is instead of just letting the 0 and infinity symbols carry an implicit limit?

>>8934101
not all limits are to 0 or infinity

and if all you write is what value you're looking at the limiting behaviour for, it won't be clear in the case when you have multiple variables that could be checked for their limit

How in the fuck do you use latex on /sci/? someone please tell me

>>8934162
It has to be enclosed in [math] tags.

>>8934162
read the sticky

Anybody have experience with NumPy?

I'm trying to use the numpy.polyfit() function to get both the coefficients for a first-order polynomial and the covariance matrix, but the covariance matrix it gives me is different from the one I calculate. I even managed to get the main diagonal of the covariance matrix to have two negative values, how is this even possible?

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>>8934183
Alright, now it's just fucking with me.

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Why do we have fear? What part of the brain handles fear? What chemicals are produced inside your brain when you're in fear? Why do some people act in fear differently than others?

I'm just wondering.

>>8934341
you'd become the food of some predator pretty quickly without fear

>>8934341
Your personality is highly dependant on your memories and experiences, so different people will react differently to the same fear stimulus because they have different experiences with them. Some might curl up in a ball because that's worked so far, while others might run away because they are confident in their physical ability. As to the chemicals, you'd have to wait here for a biologist. Or start your own thread and get shitposled to oblivion, that's always an option.

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>>8933663

>>8931639
a matrix A_p*n has an right inverse matrix B_n*p if A_p*n * B_n*p = I_p
a matrix A_p*n has an left inverse matrix B_n*p if B_n*p * A_p*n = I_n

>>8934339
post code on something like pastebin.
looks like you're dividing by zero somewhere.

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Can someone explain why we want those terms to cancel, why not the other terms and can't they cancel by having the partial derivatives equal zero as well?

>>8933842
I find quantum stuff more straightforward than special relativity, the maths of quantum all seems to fit together nicely, it's abstract but with tons of analogies to basic geometry, the physical results are just weird.
The maths of special relativity isn't tough but the situations can be much more confusing I think

>>8933573
A jack of all trades is a master of none, is probably what he meant, and if you were really serious about learning the math and physics to fully understand quantum relativity in detail, its going to take a while. It is strange that you expect to be able to do quantum mechanics without knowing even energy principles.

>>8933886
>>8933819
You two are retarded. How do you expect the function to know which board you're talking about if you don't tell it?

>>8934075
You have 2 vectors, the normal and a point on the plane
In cartesian coordinates, the coeffecients of x, y and z are the coeffecients of i, j and k in the normal, and since it passes through the origin d = 0
So you get x + 2y - z = 0

>>8934339
>>8934435
I think it has to be the polyfit function.

import numpy as np
import matplotlib.pyplot as plt
import scipy.linalg as linalg

x = np.array([0,1,2,3])
y = np.array([3.0,5.3,7.8,10.0])
sy = (y+0.5)*0.05

c_poly, cov_poly = np.polyfit(x, y, 1, w=1/sy, cov=True)

A = np.column_stack([x/sy, np.ones(x.size)/sy])
a = np.dot(A.T, A)
b = np.dot(A.T, y/sy)

c_matrix = linalg.solve(a,b)
cov_matrix = linalg.inv(np.dot(A.T, A))

print("_"*60)
print("poly:")
print(c_poly)
print(cov_poly)
print("matrix:")
print(c_matrix)
print(cov_matrix

____________________________________________________________
poly:
[ 2.35320403 2.99434068]
[[ inf -inf]
[-inf inf]]
matrix:
[ 2.35320403 2.99434068]
[[ 0.02180461 -0.01389099]
[-0.01389099 0.0273755 ]]
>>>

So:

[math]y = log_\epsilon x[/math] can become [math]\epsilon^y = x[/math]

and:

[math]\frac{dx}{dy} = \epsilon^y[/math] so [math]\frac{dy}{dx} = \frac{1}{\epsilon^y} = \frac{1}{x}[/math]

But:

[math]y = log_{10}x[/math] is [math]y = 0.4343log_{\epsilon}x[/math]

and then my textbook just jumps directly to:

[math]\frac{dy}{dx} = \frac{0.4343}{x}[/math]

without explaining how the 0.4343 got on top. I'm specifically wondering what to do with the 0.4343 in front of the logarithm, and how to calculate [math]\frac{dx}{dy}[/math] for [math]y = 0.4343log_{\epsilon}x[/math]

Can somebody pls show me?

>>8934555
In other words, does [math]0.4343log_{\epsilon}x[/math] become [math]0.4343\epsilon^y[/math] or something else? What does the [math]\frac{dx}{dy}[/math] for that look like? Is it still itself?

>>8934555
>without explaining how the 0.4343 got on top


d/dx (log f(x)) = f'(x)/f(x)

>>8934555
>>8934560

[math]y = 0.4343ln(x) \implies e^{\frac{y}{0.4343}} = x[/math]
Now do what you did above, find dx/dy, substitute and bobs your uncle

>>8934562
What do I specifically do with whatever a log is being multiplied by? What does the phrase look like right before I find the differential coefficient of it? It's not 0.4343ϵ^y is it?

>>8934563
Does the dx/dy of e^(y/a) remain e^(y/a) like with e^y?

>>8934570
It does, you surely know that [math] \frac{d}{dx}e^{ax} = ae^{ax}[/math], no?

>>8934573
Ok. Finally a really dumb question because I'm even an algebralet:

so [math]\frac{dy}{dx} = \frac{1}{\epsilon^\frac{y}{0.4343}}[/math] right?

What do I do with a fractional exponent in the denominator? I'm Googling but there are no matching examples. Clearly the 0.4343 gets up to the numerator but why?

>>8934579
You've missed the 0.4343 coefficient when finding dx/dy, look at the formula here >>8934573
After that you finish by substituting x back in

>>8934579
so [math]\frac{dx}{dy} = 0.4343\epsilon^\frac{y}{0.4343}[/math]?

>>8934589
[math]\frac{dx}{dy} = 0.4343\epsilon^\frac{y}{0.4343}[/math]

>>8934589
>>8934591
No, and stop using epsilon instead of e, the coefficient is 1/0.4343 you fucking sped

>>8934593
I don't see how you get that.

>>8934597
Look here
>>8934573
Let a = 1/0.4343
And we are done

>>8934599
>>8934599
so

[math]\frac{dx}{dy} = \frac{1}{0.4343}e^\frac{1}{0.4343}y[/math]

>>8934600
Yes, good boy

>>8934602
I don't see how it simplifies to [math]\frac{dy}{dx} = \frac{0.4343}{e^y}[/math] algebraically though. How do I get e^y by itself again so I can substitute x?

>>8932993
So if I love somebody, they must love me back?

Damn, I wish somebdoy would have told me that earlier

I am using the simplest approximation to an integral
[math]\int_{a}^{b}f(x)dx = \sum_{i=1}^{N}f(x_i)\Delta x[/math]

this just follows from the definition, but what is this method called?
in my book they just say the description, but I want to read more about it and its errors

I mean, it's even simpler than the midpoint rule
you just take the function value and multiply with the area

>>8934555
[math]\log_a x = \frac {\log_b x} {\log_b a}[/math]

>>8934654
>this just follows from the definition, but what is this method called?
Riemann integral.

>>8929294
how many different combinations of numbers are possible in a 15 base system when you have a 15 digit number but you aren't allowed to have the same digit occur twice in the number?

>>8934675
15!

>>8934678
calm down

>>8934675
>how many different combinations of numbers are possible in a 15 base system when you have a 15 digit number but you aren't allowed to have the same digit occur twice in the number?
15!, more or less 1.3*10^(12)
15 possibilities for the first number, 14 for the second one (15 minus the one already used), 13 for the third one, and so on.

>>8934680
>>8934678
thanks

>>8934667
fuck, now I feel stupid
thanks though

(atm) what are the chances that hawking radiation is true?

You have 5 row vectors and each one has 5 elements.

You need to pick an element from each one of these 5 vectors and form a new vector from it.

You must do this for all combinations of element indexes. Thus you need to do this 5^5 times. What is the most efficient approach?

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My galvanic cell is generating less potential than it should what could be wrong?

Does anyone have links to a good tree of life phylogeny that's up to date on the internet? Just the vertebrates would be good enough. The Tree of Life Project website seems out of date all over the place and claims it hasn't been updated since 1995.

>>8934988
I was looking for a similar thing a few years ago, when I was really into biology
I found nothing then, I basically had to look up sources on wikipedia and make the relevant trees myself

it's sad that this has not happened yet
a full encyclopedia with all entries from our current knowledge
with disclaimers whenever there is disagreements in the science community etc

Is there any reason to use a PTC thermistor over a PT100 sensor?

>>8934678
>>8934680
>>8934683
Incorrect, its 14*(14!), the leading digit can't be 0

Is there a special word for numbers like the following?

1, 10, 100, 1000, 10000, 100000, etc

Assume it's any base. The idea is that a single bit is on, so in base ten, it's a "clean" number. Rather than "one hundred and twelve", for example, 100 is just "one hundred". Rather than 34 being "thirty four", 30 is just "thirty"

Is there a special word for these... 'demarcation' numbers?

This is a test.
[math]\Gamma(z):=\int_0^\inf x^{z-1}e^{-x}dx[math]

>>8935383
powers of the base

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>>8935384
you can test with the TeX button in the top left corner of quick reply

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About to be the first person in my family that has gone to college, and additionally passed calculus 1. It may not seem like a big achievement to you, but I never imagined that I would be here.

Thanks for all the help these past few months. I think that I'm going to do poorly on the related rates problems, but I only need to get a 56.5% on the final to pass the course.

>tfw professors had to help me apply to transfer to universities because I didnt even know that you needed to do it
>tfw no grants or loans or any financial aide at all even though I'm the first one on both sides of the family to go to college/uni
>tfw no idea what I'm doing
being a brainlet is hell, wouldn't recommend it if you had the choice

>>8935383
power of 10, power of 2 etc.

>>8935395
Test
[eqn]\oint_{\partial S}\mathbf{B}\cdot d\mathbf{l}=\iint_S(\mu_0\mathbf{J}+\mu_0\epsilon_0\frac{\partial\mathbf{E}}{\partial t})\cdot d\mathbf{S}[/eqn]
[eqn]\nabla\times\mathbf{B}=\mu_0\mathbf{J}+\mu_0\epsilon_0\frac{\partial\mathbf{E}}{\partial t}[/eqn]

>>8935390
>>8935432
I *JUST* figured this out a minute ago and decided to tab in just now. I was rewriting a comment on my code describing what my method did when i realized that "returns the largest power of ten that's also a factor of the number" means... yeah. 'base' keyword helps

thanks!

There were threads here some weeks ago, about a "breakthrough" in batteries technology, by John Goodenough. Is there a peer review out?

Is it worth researching in a different area of study (that I'm not sure if I will be working in the future), just to say that I did?

>>8935463
Those are some nice equations you have there, it would be a shame if magnetic monopoles were to happen.

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I don't understand eigenvalues and eigenfunctions.
How do we guess/calculate or anything?

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How do I deal with brain frog? After I dropped out highschool I wasted my self on drugs and alcohol and now I'm starting to study again but I can't grasp even basic concepts even though I was quite the ace of school. Idk how to say this but it feels like I have been dumbed down, is there a way to recover from this? How do I feel smart again? Is it just a lack of practice? What do I do? If you're going to suggest stop being a depressive alcoholic it's out of the question unfortunately.

Is it possible to trivially define complex objects? For example, to define A and B to be A and B, but in such a way that something else could be just A or just B non trivially?

if f and g are functions, what's the codomain of f+g? is there a convention?

any book to learn linear algebra?

>>8935753
f+g is usually only defined when f and g have the same codomain

>>8935646
depends on the function and system you're working with

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Is the speed of electrons constant in a circuit? I mean, I was looking at diagrams and everything, and they say the voltage of a circuit comes from say batteries. And the circuit only exists because electrons are being repelled by one end of the battery and attracted by the other. So wouldn't that make the current slower right in the middle of the circuit, where an electron would be the farthest from both positive and negative side of the circuit?

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Ultra brainlet here. How do I not do shit in Calc 1? Math is fucky for me.

>>8935769

Why is there so much fuzz about voltage? Current is the flow of charge, not the actual electrons as I understand it.

>>8935810
the electrons are the charge

>>8935790
https://www.youtube.com/watch?v=rjLJIVoQxz4

1,1,3,1,5,3,7,1,9,5,11
What is the pattern here?

>>8935859
1,2,3 etc with all factors of 2 removed

I'm taking real analysis, abstract algebra, number theory, and a class on mathematics of finance this fall. With such a heavy courseload I want to try to get a headstart this summer. I don't know what text books we'll be using yet. How should i prepare? Skim chapters?

Please don't call me a brainlet

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where the fuck does the 2pi() come from??

>>8935700
I used to do a lot of drugs in highschool, smoked weed pretty much every day, dropped acid and took shrooms pretty regularly as well. When I finally quit I felt pretty fucked and had trouble with self studying. I took some CC classes and failed all of them. I decided to study really hard for my classes and have really been improving. I feel a lot better than I did, and this last semester I got pretty much 100% on all my assignments and tests in Calc III and was top of the class on every test in physics. looking back on it I think I was just being a bit of a bitch and blamed drugs for problems I already had before that.

for me persistence was the only thing that I was lacking, I stopped smoking, drank only water and studied my ass off. I don't think drugs, smoking and drinking was negatively affecting me all that much looking back, but learning to kick all that really helped me to start studying seriously

>>8935872
>I don't know what text books we'll be using yet. How should i prepare?
email the prof and ask

>>8935878
what do you get when you did the integral?

>>8935898

instead of the 2pi(), I got 2sin(+oo) and 2sin(-oo)... everything else is the same

>>8930232
these are acute symptoms of a depletion of serotonin in the brain, talk to your doctor about obtaining sildenafil, or eat some aloe vera

>>8935903
>2sin(+oo) and 2sin(-oo)
That hurts to read

>>8935753
First, you need to have [math]\text{dom}(f)=\text{dom}(g)[/math] and [math]\text{cod}(f)=\text{cod}(g)[/math], and the tricky part comes next. You can't have any set, as you don't necessarily have an addition defined in it, and this means (I'm saying this because I don't think you've studied much abstract algebra) that [math]a, b \in S \Rightarrow a+b\in S[/math], and so it can't be any finite subset of the complex numbers with the ordinary addition unless it both functions map everything to 0, and 0 is in the codomain.

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>>8935959

If a function is differentiable, does that imply that it is differentiable to any nth degree, also, how might you go about proving this?

>>8935968
no, it could just be once differentiable

>>8932860
rohypnol or become a girl

>>8935996
What are some good examples of this?

>>8936006
x^2sin(x) is just diferentiable once at 0

>>8935968
No. Only analytic functions are infinitely differentiable. Proofs in complex analysis books.

>>8935646
https://www.youtube.com/watch?v=PFDu9oVAE-g

What happens when two stars collide?
Will they explode and leave nothing behind, become one bigger star. a black hole or?

>>8936087
Nigga, there are plenty of C^infinty functions that arent analytic.

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>>8929294
What's the mathematical name for the shape that looks like rectangular pillow, in which the thickness is at a maximum in the center, and approaches zero toward the edges?

>>8936187
a closed ball

>>8935968
it's always good to have examples. [math]\sqrt[3]{x}[/math] is not differentiable. if you take the antiderivative k times, you will get a function which is differentiable exactly k times.

>>8936196
Is there a term specific to a closed ball with a rectangular profile?

>>8936202
You're kidding right?

[eqn]\frac{d}{dx}x^{\frac{1}{3}} = \frac{1}{3}x^\frac{-2}{3}[/eqn]

>>8936219
at x = 0

>>8935411
just a quick update i did it

>>8936219
a differentiable functions means differentiable at every point in its domain. tell me what the derivative at x=0 is.

>>8936309
You didn't specify the domain:^)

is there a magic trick you can use to count from zero to 1 thousand without ever getting a number that has repeating digits?

Im currently starting to read up on image processing with java

what kind of math is used to optimize a picture? i want to be able to map a column using a function f(x,y)

>>8936407

can it be consecutive? like is *xx* acceptable? or only xxx... not acceptable?

is cognitive science a meme? Is it worth diving into if I am interested in philosophy and programming?

Anons what's the word's equivalent to latex's smallextended?

I understand how you can determine that two sets have equal cardinality by providing a bijective function, but am I the only one who is bothered by the fact that the set of reals in intervals [0,1] and [0,2] has the same cardinality?

>>8929294
why are the chips labelled 'sips'?

>>8936313
It's assumed the domain is the reals by the context of the question, you're genuinly retarded and should kill yourself

>>8936691
>am I the only one who is bothered by the fact that the set of reals in intervals [0,1] and [0,2] has the same cardinality?
Probably. Does it bother you that [math]\left |\mathbb{Z} \right | = \left |\mathbb{N} \right |[/math]? If not, it should bother you even less that every real interval has the same cardinality seeing as its a complete set

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HOW THE FUCK DO I FUCKING SOLVE THIS FFS?!

The answer is 4, so just transforming the -1 <= x <= 1 part is not gonna fucking cut it.

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How the fuck do I find the median of the first 9 whole (negative, zero and positive ffs) values of the range? There's fucking x there, so how the fuck do I know the fucking range? I tried all sorts of "first 9 whole values", but it doesn't fucking give me what they want, which is zero.

>>8936704
it's adorable

>>8936934
Set it equal to a value, then square both sides, should give you a good start
Pro-tip: Squaring surd functions a lot of times tends to give degenerate solutions, so check them at the end

>>8937006
Have you tried... actually solving the integral?

>>8935968
consider x^2sign(x). the derivative is 2|x|, which is not differentiable at the origin

>>8936014
>>8937363
For the love of fuck, use latex or brackets

Why are imaginary numbers treated like some weird, complex(pun not intended) thing? Aren't they just a way of writing coordinates? I don't see how they could be viewed as this unimaginable(put not intended) quantity, when they are never actually used to mean a quantity.

>>8934166

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>>8936934
Here is my terrible working. Since sqrt (x + 3) - 2 is always negative, its modulus value is 2 - sqrt (x + 3).

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How long would it take to complete the following:

Algebra and Trigonometry - Judith Beecher

Elementary Calculus - Keisler

Matrices and Linear Algebra" by Schneider and Barker

Please help a brainlet understand.

x + y = 100%

There is 49.18% more x than y. Find percentage of x. I know the answer is 74.5% and I know which numbers to plug in to get the answer but I don't get the thought process for the solution.