SQT - Stupid Questions Thread

>>8135619
Girls und panzer?

This is my question. Let's say I have x=cos t and y=sin t, and I'm asked to plot from 0 degrees to 60 degrees, get the equation of the tangent when t=20 and lots of other stuff like that.

What's the name of the topic I gotta lookup to find this stuff? It's related to vector calculus.

is it worth pursuing a degree in chemistry? i've realised i love it, even the incredibly boring bits

>>8135617
>not posting Ferris Wheel-sama or the fucking Finns

I'm going through some of Chen & Duong's Elementary Mathematics papers and began to second-guess my self on some combinatorics problems.

"How many ways can you choose 12 people out of 20 and seat them in a circle?" Straight forward. Seat the first, and all seatings afterwards are relative to this first seat. P(19, 11) is the solution.

"How many ways can you choose 12 people out of 20 and seat them along the sides of a square with 3 people on each side?" This also seemed straight forward at first. You seat any three people (P(20, 3)) on a side, and seat all others relative to them. All other seatings are relative to this side, so there is P(17, 9) possibilities, since there are 17 people and 9 seats left to choose from.

Then I began to think that it wasn't so similar to the first question. First you seat the first 3, P(20, 3), and the rest of the seatings are relative to that, then you pick the next side P(17, 3), and the rest are relative to that, then the next side P(14, 3), and finally P(11, 3) is how many are left to pick for the last side.

This answer doesn't quite sit right with me either, but it got me out of balance enough that I no longer feel comfortable with the first solution either. Which method and answer is correct, or is there something else that I missed?

>>8135708
Oh, I think I might have got it now. For every ordering of 12 people along a square with 3 per side, there will be 4 duplicates: the result of rotating each side clockwise. P(20, 12) / 4. Now I think I got the circle one wrong. Is that just P(20, 12) / 12? That doesn't come out to P(19, 11), but I feel like that also makes sense. After seating one person in one seat you would have 19 people left to choose from and 11 more seats.

>>8135708

There are 125970 ways to choose 12 out of 20, and 6.0339832x10^13 ways to choose 12 out of 20 and then sit them along the sides of a square with 3 people on each side.

The first problem is just about combination, but the second is about permutations.

>>8135817
Ordering counts for the first one, it's not just "how many ways can you choose 12 people out of 20", it's how many ways you can arrange them in a circle.

6.0339832x10^13 is P(20, 12), but wouldn't we also have to divide out duplicates, of which there are four? There's some N number of permutations or arrangements, but of those permutations, some of them are the same ordering of K people rotated such that the same three people are grouped together, but on the next side counter/clock-wise.

>>8135840

Jesus I just asked Cortana but you sound smart, I guess you should trust in your instinct dude.

>>8135673

Lad, chase your dream.

>>8135673
I am finish up a degree in chemistry. I have about 2 more labs and physical chemistry 2. I would say yes but follow your dreams as long as they're not stupid dreams.

My question:
Why is the kernel of a homomorphism useful and how does it tell you the amount of information lost?

>>8135872
Thanks m8

>>8136085
I'm sorry but I don't think this is helpful. Thanks for trying, though

>>8136091

Yeah I'd rather share a female with other man than to be a butthurt basement dweller that can't get a GF like you DESU SENPAI.

>>8136099
>projecting this hard
your post says more about you than me 2bh

>>>/wsr/138495
Question about eigenvectors/values

How can I prove that
[math]\sum_{n=1}^{\infty} \frac{\sqrt{n^2+1} - \sqrt{n^2-1}} {n}[/math]
converges?

>>8136174
1. Correct, by definition, an eigenvector has to be non-zero.
2. Also correct; any vector that is the result of the product of an eigenvector and a scalar is also an eigenvector.

>>8135624
Differential equations of curves. I recommend reading Carmo.

Is living forever really a question of turning off a couple genes or is sustaining life Àctually more degrading of a process when in motion than that?

>>8136206
I would try to consider that series as An and either try to prove that a series Bn converges and that Bn is > An, or try to assess the limit of A(n+1)/An

>>8136218

There's some shit substance or whatever in your ADN that wears out with every replication. As that shit further depletes you become more fucked up (AKA old) and you die.

>>8136221

Because you touch yourself at night.

>>8136206
Thanks

File: Screenshot from 2016-06-10 23-32-09.png (28KB, 521x367px) Image search: [Google]

28KB, 521x367px

>>8136206
Have a pretty solution anon :)

>>8136239
Thanks anon.

>>8136085
I'd probably be worse off if I followed this

Somebody actually believed this was good advice

Where are all of the science startups? Why does tech get it all?

>>8135884
The kernel of a homomorphism is useful for the First Isomorphism Theorem which allows you to say two groups are isomorphic (functionally the same) https://en.wikipedia.org/wiki/Isomorphism_theorem.

The kernel tells you how much information is "lost" because it tells you what elements are mapped to the identity, if it is more than just the identity in the kernel some of the information is "lost".

File: stuff.png (17KB, 675x104px) Image search: [Google]

17KB, 675x104px

I got pic related from:

http://math.stackexchange.com/questions/495067/finding-the-velocity-with-parametric-equations-for-the-position-of-an-object

Now let's say that I solved it just as the image said and got v = (x,y) where components x and y are f(t). I'm asked for speed when t=50, Does this mean to just input 50 in every t in (x,y) or do I have to do something else? The result could be a plain number like (7,5) with no xs or ys or anything and I'm not sure if that could be right.

>>8136446
it's asking for the speed so you plug it into the last line of your pic

and yes you just plug in t = 50

Why don't electrons fall into the nucleus?

>>8136472

I wondered the same thing like a week ago and based on my experience with KSP my conclusion is that they don't fall because they're spinning really fast.

>inb4 but why are they spinning
>inb4 how come they don't ever stop spinning

Yeah those are good questions but you're asking the wrong dude.

>>8136476
>I wondered the same thing like a week ago and based on my experience with KSP my conclusion is that they don't fall because they're spinning really fast.
First, spinning is a misleading word, orbiting would be much better. However, your suggestion is one of the earliest models of the atom, and has a big flaw: the orbits would decay towards the nucleus without energy constantly being given to the electrons. Here, from wikipedia:

>Unlike the plum pudding model, the positive charge in Nagaoka's "Saturnian Model" was concentrated into a central core, pulling the electrons into circular orbits reminiscent of Saturn's rings. Few people took notice of Nagaoka's work at the time,[14] and Nagaoka himself recognized a fundamental defect in the theory even at its conception, namely that a classical charged object cannot sustain orbital motion because it is accelerating and therefore loses energy due to electromagnetic radiation.[15]
https://en.wikipedia.org/wiki/Atomic_orbital#Early_models

>>8136472
See the same wiki page for history of moving to newer models.

File: skid.gif (2MB, 320x179px) Image search: [Google]

2MB, 320x179px

How do you study for something that isn't tested?

Basically I want to start learning a new topic and have found a few highly recommended text books. The problem is, for now I don't have anyway to pinpoint which topics are of most importance nor do I have an opportunity to apply that knowledge on any realworld cases.

So what do you do to study topics outside of Uni?

I'm curious about consumer habits of manufacturing company owners.

especially if they consume their own products.

where can I get this kind of information, other than interviews and celeb news, because I dont really want to dig through all that bs

File: vortex_in_vortex_out.gif (36KB, 398x376px) Image search: [Google]

36KB, 398x376px

>>8136472
because the center is empty!

File: 1357627729258.gif (310KB, 360x240px) Image search: [Google]

310KB, 360x240px

Including experimental technology that might see significant development in the near future like fuel cells, what's the most efficient solution to portable electrical power? Not internal combustion generators I assume.

>>8136405
thank you very much.

My question is the last one from the previous thread, refined slightly.

If you have 2 planets orbiting a star at relativistic speeds in opposite directions, 0.5 c each, would time dilation affect a clock sent from one to the other? Which planet would have a faster clock?
Does acceleration affect time dilation at all or is it only speed? Does the direction matter or is it only speed?

Appreciate any help

>look at scholarship application for college
>In no more than 500 words, please tell us about yourself including your academic goals, your career aspirations, and what makes you unique.

Computer Engineer here. Someone write me an example paragraph of what to write.

ok to preface this im a huge retard who knows nothing,
But since we live in 3 dimensions right, do we live in a "sphere" or is that my brain trying to perceive 3 dimensions?
and if we do live in a sphere right how can we actually have on a dimensional sense straight lines?

>>8136950
no we live in a square

>>8136943
things about yourself
things about your academic goals
things about your career aspirations

apparently nothing makes you unique so don't bother with that part

>>8136959
Wouldnt we live in a cube?

>>8136950
Kek dimensions are variables which we assign physical meaning to. Since any position in space can be described by 3 dimensions, we are said to live in a 3 dimensional space.

>>8136582
so then where are the neutrons and protons? Are they in a superpostion?

Say, I have a linear differential equation of a higher and I'd like to laplace transform it to solve it, but I don't know y(0), y'(0) and so on, is it possible to solve it using Laplace transforms?

Obviously not, right?
I could evaluate an integral of the same structure the Laplace transform, i.e. e^(-sx) starting at the first x value I do know, but where would I go from there?

Basically, how do I find the "inverse transform" of any complex valued function?

>>8137349
no, they're just really really small.

what does the dx means in an integral calculus?

im starting with maths.

>>8137462
nobody knows
people just put it there to remind you that you are integrating in respect to x.

>>8137462
Riemann integration: it is notation and nothing more
Later on: it is a measure

Just give it to me straight /sci/, will we be able to bring back any living dinosaurs in my life time?

>>8137487
no

>>8137140
oh so because i am human, I am attributing geomtry to variables.

>>8137467
Not him but I think this actually ties something together for me.

Riemann argued that we didn't need axioms of Euclid to do geometry, that we could do geometry in any space so long as we can measure. So if we are working in curved space, we can integrate to get length.

So is a measure space a set of points with some sort of relation defined so that we can take measurements? I imagine I am very imprecise with my description, but am i on the right track?

>>8137522
>So is a measure space a set of points with some sort of relation defined so that we can take measurements?
Yes. I'm personally not particularly far into this material, but here's the wiki page: https://en.wikipedia.org/wiki/Measure_(mathematics)

>>8137349
correct
>>8137432
no

File: Untitled.jpg (79KB, 917x641px) Image search: [Google]

79KB, 917x641px

What is it about x3 that makes it a free variable? Is it because both x1 and x2 can be defined in terms of x3?

>>8136395
where do you sell science?

>>8136950
3 dimensions just means 3 degrees of freedom; you can move up/down, left/right, and forward/backward
"living in a sphere" doesn't make much sense to me, not sure what you're trying to ask

>>8137688
You can re-define that so that either x1 or x2 are free variables.

File: 1465689460561.jpg (129KB, 1044x1360px) Image search: [Google]

129KB, 1044x1360px

Where can I download this book? I couldn't find it anywhere.

>>8137845
So why must at least one be a free variable? Does it have to do with linear independence

>>8137885
In reduced form you have a row of all zeros, which does imply linear independence, yes. In this case it means your answer is independent of one of the variables. He says X3 because it's the third row that's free (all its saying is 0X1+0X2+0X3=0, so it's trivial), but though row operations you can easily make X2 or X1 the free variable.

What is the difference between arcsin and csc?
I know arcsin is sin^-1 (x) and csc is sin (x)-1, but when would they be different?

>>8137933
and row reduction.. to my understanding when doing row reductions we are getting different matrices, but each matrix from the initial and all of the intermediates to rref all have the same solution set? do they still affect any given vector in the same way?

>>8137933
why is it in the picture we need 3x3 matrices to do the transformations despite our object (vectors) is in R^2

File: b64d88b5898ffff0885db0ff9f1ccb27.jpg (97KB, 736x981px) Image search: [Google]

97KB, 736x981px

>>8138009
oops

>>8138011
The reflection about the origin is actually a 90 degree rotation. The F would face the opposite direction.

>>8138025
And today anon learned that composing x-reflect with x-reflect is equivalent to rot-90. Congratulations to you.

>>8138029
Every rotation can be decomposed into two reflections, not just 90 degree ones.

File: endmylife.png (76KB, 1152x889px) Image search: [Google]

76KB, 1152x889px

How would one find the overall structure here?

File: ss+(2016-06-13+at+03.14.22).png (4KB, 343x235px) Image search: [Google]

4KB, 343x235px

>>8138516
Would it be this?

>>8138011
Notice how in all of them except the translation you have 1 in the lower bottom corner and zeros in that row and column. This means nothing is changed in the z direction so you're right you don't. For translation you need it cause you can't map (0,0) to anything other than (0,0)

>>8135624
> I'm asked to plot from 0 degrees to 60 degrees
parametric equations
>get the equation of the tangent when t=20
parametric differentiation
>and lots of other stuff like that
parametric stuff like that

So with AC, every set can be well-ordered
The set together with the order relation forms a category, does it not? This seems to be the easiest way to make a category out of a set.
So what is the best way to do this without AC?

File: DontUnderstand.png (387KB, 1274x203px) Image search: [Google]

387KB, 1274x203px

P is a pmf, X&U are random variables whereas x is distributed by f and f(x)<Mg(x) for some constant M and g being another distribution (supp(f) is a subset of supp(g) w/e that is supposed to mean)

>>8138927
Sorry for double posting, the question is, why are these equal. Bayes Theorem and the theorem of total probability don't fit imo

How do get surplus power from a tokamak?

>>8138688
can you not just take a finite subset of Z ?

>>8138929
Second to third is just the definition of conditioning. First to second probably has something to do with the definitions of X, Y, and U.

I read recently that mass in physics pertains to the second cohomology class of the lie algebra of the galinean group.
The second cohomology group [math] H^2 (\mathfrak{g}, M) [/math] over a module M, is the space of equivalence classes of lie algebra extensions. Can a physicist explain how the pertains to mass (I'm much more of a mathematician)?
I was wondering if anyone on here could offer an intuitive explanation and perhaps give a reference to where one could read about or see the origination of this result (my searches haven't uncovered anything promising).

File: asdasd.png (5KB, 424x35px) Image search: [Google]

5KB, 424x35px

My math skills aren't great, can someone tell me how this was done?

It's a random step in a DE problem, i just don't get how +c became *c.

>>8137430
> Say, I have a linear differential equation of a higher and I'd like to laplace transform it to solve it, but I don't know y(0), y'(0) and so on, is it possible to solve it using Laplace transforms?
If you don't know the initial conditions, you just treat them as constants, which gives you a family of solutions with the initial conditions as parameters.

E.g. consider an undamped harmonic oscillator:

x''+ω2*x=0

The Laplace transform is

s2*X(s) - s*x(0) - x'(0) + ω2*X(s) = 0

Solve for X(s):
X(s) = (s*x(0) + x'(0))/(s2 + ω2)
= s*x(0)/(s2 + ω2) + x'(0)/(s2 + ω2)

The inverse transform is
x(t) = x(0)*cos(ω*t) + (x'(0)/ω)*sin(ω*t)

>>8139113
[math]\ln | T - 70 | = kt + c_1 [/math]
[math] \exp (\ln |T-70|) = \exp ( kt + c_1 )[/math]
[math] T - 70 = \exp(kt) \exp(c_1) [/math]
Let [math] c_2 = \exp(c_1) [/math]
[math] T = 70 + c_2 \exp(kt) [/math]

>>8139113
That's how logs work:
ln(a*b)=ln(a)*ln(b)

>>8139113
a^b+c = a^b * a^c in general

Nigga i'm in community college goddamn get your shit together.

>>8139118
thats grate, ty.

i thought it was something like that, but i didnt see they just made c2 = e^c1.

tanks again :)

>>8139130
yeah it's a pretty common technique.
Try deriving the damped, harmonic system via the linear differential equations method and you get to do it a bunch of times.

Show:

[math]\operatorname{Spec} R + \operatorname{Spec} S = \operatorname{Spec} \left( {R \times S} \right)[/math]

>>8139153
is exp(kt+c) the same as exp(kt) + exp(c)?

>>8139177
No its the same as exp(kt) * exp(c)

>>8139181
if exp(x)*exp(x) = exp(x+x), how would you get exp(x^2)?

>>8139187
exp(x)^x

File: what am i looking at.png (21KB, 855x157px) Image search: [Google]

21KB, 855x157px

The answer to all of these is NO but i thought they were all yes.

I just dont understand :( Why is they no?

>>8139307
try to answer this: why are they "yes" in your opinion? Try to prove it.

We will point out your mistake if you don't find it.

>>8139307
A subspace satisfies the requirements of a space, such as being closed under addition and scalar mult, and containing zero. The first is curved, so it is not closed under addition, it is easy to find two vectors that satisfy the equation which add to a vector that does not. The second would be acceptable if it passed through the origin, but because multiplying a vector by 0 yields a vector that does not satisfy the equation, it is not a subspace. Finally, the third is a sheet that fails for the same reason as the first.

>>8139307
For the first one, S would not even be a space.

Consider the pair (1,1) and (2,8). They are both elements of S but if you add them up they equal (3,9) and 9 is not 3 cubed. Therefore that set is not closed under linear operations and thus is not a space.

The same goes for the second S. It is not closed under linear addition.

Same goes for the third one apparently.

These are all trivial exercises, just look for counter examples.

>>8139311
well my reasoning was the same for all of them :(.

i think i might just not understand what all the symbols mean.

can you convert one of the questions to words?

I dont really get what S = {...} really means in words.

Like for 1. why cant x =1 and y =1 to give 0 be valid?

>>8139307
Look at your definitions. You should have a list of properties a subspace must satisfy. Either try and prove that it satisfies them or try and find a counterexample.

I'm not sure about the context but it looks like it's referring to subspaces in the context of vector spaces. In that case one of the rules is that the 0 vector of the original space must be contained inside the subspace. It would seem that the second set fails that property since (0,0), i.e. the zero vector of R^2, is not contained inside S (0-3*0 = 5 is provably false).

>>8139328
>I dont really get what S = {...} really means in words.

S is the set of ordered pairs of the form (x,y) which are elements of the real plane, such that the elements of the ordered pairs satisfy the equation x cubed - y = 0

in your case indeed x=1 and y=1 are part of that set.

>>8139316
sorry but why does it being curved mean its not closed under addition?

>>8139338
By the way you have been communicating I can sense a lack of fundamental understanding.

Do you know what a space is? A subspace is NOT a subset. In your case all of those sets are SUBSETS of R2 and R3 and whatever but they are not subspaces.

Do you understand the fundamental difference between these two structures?

>>8139332
im confused what that equation (x-3y=5 as 0-3(0)=5) would look like visually. does that mean any equation that has an answer that isnt 0 is not in the subspace?

>>8139345
>ny equation that has an answer that isnt 0 is not in the subspace?

The elements of that space are not equations.

Do you know formal set theory and linear algebra?

>>8139343
i dont think so, and i get span confused too. :(

>>8139348
im trying to learn linear algebra but its confusing. i was almost ok with matrices and gauss jordan elimination, and then they went to spaces and spans and subspaces

and all the symbols are confusing

>>8139350
>i dont think so

Then just pick up a basic linear algebra book. Don't pick any one which markets to CS majors because those will probably start you up with matrix operations. Look for a mathematically rigorous one.

>span confused too. :

The span of a set of vectors is the space that those vectors generate by way of linear operations.

But if you do not know linear algebra then you have no idea about what I am talking about here.

>>8139351
Just re-read those definitions and if you don't get them then it might be sensible to downgrade your studies to elementary set theory because without set theory you will never be able to read a mathematical statement.

>>8139172
By + do you mean [math] \oplus [/math] ? And by = do you mean [math] \simeq [/math] ?

>>8139378
>By + do you mean ⊕
No I mean +.The topological sum. i.e. disjoint union

>And by = do you mean ≃
yes

>>8139276

File: 26.png (12KB, 774x159px) Image search: [Google]

12KB, 774x159px

no clue how to do this

next q is on cauchy-riemann conditions so I can't use those for this

is it literally just df(x,y)/dz* = dF/dz* = 0 -> F= F(z)?

>>8140407
put f(x,y)=g(z,z*)

now becouse derivative of g respect to z* is zero, then it must be that g in only function of z, i.e F(z)

File: vertical.png (2KB, 277x152px) Image search: [Google]

2KB, 277x152px

How does that x get into the second equation?

Probably gonna get no replies but whatever.

Let's say I have a compact manifold M, and two framed submanifolds N, N'. I'd like to show where they intersect, there exists a homotopy that deforms N slightly so that they intersect transversally.

Trying to show existence using the fact that framed submanifolds have neighborhoods that behave like a cartesian product and that orientation preserving diffeomorphisms of open subsets of Rn are smoothly homotopic to the identity.

In a neighborhood of the intersection I'd like to use product representations of N, N' in such a way that we can smoothly deform the parametrization of N' so that it agrees with the normal frame we're given for N but I'm not sure if that's possible or even the right approach.

File: image.jpg (1MB, 3264x2448px) Image search: [Google]

1MB, 3264x2448px

Okay, so this is a line l. It passes through points (a, a2) (b, b2) of the parabola y=x2. b>a
I was asked to find S1, so I did, it's 1/6 (b-a)3
Then I was asked to find a in terms of b if l is perpendicular to the tangent line at b. It's (-1/2b) -b.
It says when 2 holds true, fins the minimum area of S in terms of b, for what value of b is the area simplified?
I'm really sorry for asking, but I asked a smart friend of mine and he told me that it's minimizes when b=a, is that true? I thought I had to derive S and set it equal to zero everytime, can anyone explain, please?
Thanks

>>8140474
>Probably gonna get no replies but whatever.
Have a (You) friend

>>8140456

What would x be to make them equivalent?
Maybe that's an implied substitution they doing. You can probably figure it out if you have def of tan available.

File: chirper.jpg (26KB, 500x462px) Image search: [Google]

26KB, 500x462px

Do mini dinossaurs feel cold on their stick feet? It breaks my heart to see the chirpers tap dancing on the ice at 7 AM

File: 2016-06-13-201835_1156x226_scrot.png (66KB, 1156x226px) Image search: [Google]

66KB, 1156x226px

I don't get it, I though water molecules had polar forces., thus, making it not electrically neutral

>>8140723
they have sensation, but limited. captive dinos loose toes all the time and it doesn't bother them a bit.

>>8140758
isn't oxygen 6 and hydrogen each one? that makes 8, god bless the bed i lie on. the charged hydrogens bend toward each other for some reason, so the molecule could be reoriented by a nearby charge.... this doesn't mean the molecule could carry it though.

>>8140842
water has a tetrahedral shape because it has 2 nonbonding pairs which are less stable than the 2 O--H bonds, causing them to be pushed closer together to maximize the distance between nonbonding pairs.

File: WestboroFaggetChurch.jpg (21KB, 400x300px) Image search: [Google]

21KB, 400x300px

>>8135617
Just watched this faghat's spooky physixs ted blab.

He mislead me to believe that a third quantum state could be tied into an entangled pair after they are already split. this is crap. the third particle can only adopt and boost-transmit the original entanglement of the two... right?

More than 1 quantum state can be given at the birth moment of the entanglement, but not afterward. If the third wheel can bring in a second state or even influence the chances of the original state's outcome, then we have faster than light non-randomized intentional information transmittal.

Again, i'm pretty sure the answer is just fuck this guy for the misleading colorcoding.

I'm starting graduate school this fall and one of the courses during my first semester is Cognitive Neuroscience. It's been a good year-and-a-half or so since I've taken any course involving the subject and I have awful severe memory problems.

I was considering emailing my professor to ask something along the lines of "Hi, future student, want to study and refresh myself, blah blah, could you give me any guidelines or specific subjects to review and go over?" I'm already planning to study neuroanatomy but I'm not too sure how in-depth I should get into it. Anyhow, would contacting the professor about this be more of a "Hey, this student is showing interest, let me give him some advice" or would it make me come off as a dumbass?

Can a galvanometer be considered an ammeter?

>>8140456
Clearly that's a ballistic trajectory expressed as a parametric curve, i.e. x and y as functions of t, where v0 is the initial velocity and alpha (a) is the elevation.

x = v0*cos(a)*t
y = y0 + v0*sin(a)*t - g*t^2/2

The first equation in your pic is derived from the equation for y (by subtracting y0 from both sides).

The second is derived from both equations. First, the equation for x is solved for v0:
x = v0*cos(a)*t
=> v0 = x/(cos(a)*t)

This is then substituted into the equation for y:

y = y0 + v0*sin(a)*t - g*t^2/2
= y0 + x/(cos(a)*t)*sin(a)*t - g*t^2/2
= y0 + x*(sin(a)*t)/(cos(a)*t) - g*t^2/2

t cancels:

y = y0 + x*sin(a)/cos(a) - g*t^2/2

sin(a)/cos(a) = tan(a):

y = y0 + x*tan(a) - g*t^2/2

Solve for t^2:

y-y0 = x*tan(a) - g*t^2/2
g*t^2/2 = x*tan(a) - (y-y0)
= y0 + x*tan(a) - y
t^2 = 2*(y0 + x*tan(a) - y)/g

>>8140929
Yes, if it's calibrated as such.

A passive voltmeter is a galvanometer with a series resistance while a passive ammeter is a galvanometer with a parallel (shunt) resistance. In each case, the resistance serves to decrease the sensitivity (i.e. increase the full-scale deflection).

With no resistance, a galvanometer can be used as either a voltmeter or an ammeter (although it's less likely to be useful as a voltmeter due to its high sensitivity and low resistance).

So i'm a retard going into CC because I couldn't get into any universities. I'm planning on getting a general transfer degree, then transferring to UW or WSU for chemical engineering.

I will probably have to take some general physics in CC, and never did physics in HS. Will I be out of my league and should I prepare in any way? Any recommended reading material? I took AP Bio, AP Chem, and AP Calc BC

This is more of a reference request. Being as cheapstake as I am, most of the textbooks I buy are international editions. Is there a website where I can find the actual differences between the international and 'regular' edition of a book?

Most of the books are pretty much the same, but some lack one or two chapters. I haven't been able to find information about international edition textbooks on publisher's website.

have this problem:

>There are 24 unique items in a bag
>I pick up an item, check what it is and write it down.
>I put the item back in the bag.
>I pick up another item, check what it is and write it down.
>I put the item back in the bag.
>I do this for a total of 102 times.
>What's the probability that I haven't gotten every unique item at least once?


My attempts were futile. I get it that the first draw, there's a probability equal to 1 of getting a unique object. On the second draw, there's a probability of 1 - 1/24 to get an unique ball. But then it branches into 2 possible paths: you may have gotten the same object, and the next draw you'd have the same 1 - 1/24 probability of extracting a unique object, or you may have gotten a different object and have a probability of 1 - 2/24 next attempt. I don't know how to generalise this into a formula...

File: solveforM.png (7KB, 220x93px) Image search: [Google]

7KB, 220x93px

I asked this like a week ago, got a response, however, I just didn't get it.

Can somebody just tell me how to solve for M?

>>8140911
Send it, it makes you look interested plus it sounds like it would be useful if he responded.

File: please help.png (3KB, 297x79px) Image search: [Google]

3KB, 297x79px

Can someone help me solve this DE?

I have no clue what to do with it, it's not separable, linear, exact, inexact, homogenous, or berenoulli.

What is it? :(

>>8140911
did that once, the prof just copypasted the required notions for his course.

>>8141898
if I remember my ode class correctly, I think you have to set u=x+y, then find du/dy from there I think

>>8141898
Take u=x+y to be your new dependent variable, use chain rule to get du/dx and from there its easy

>>8141469
Is this an assignment, do you know the solution? Should this be solvable by hand? I haven't taken any probability since high school but I thought I'd give it a try.
Warning: This might be retarded. I thought about the sequence of picks you had to make and the different order you can make them.
First you pick the first unique object with probability 1, then you can either pick that object again X times or pick the next unique object. After picking the next unique object you can pick that one or the first object again Y times or pick the next unique object. The expression for the probability of such a sequence of picks is then:

P = 1 * (1/24)^X *(23/24) * (2/24)^Y * (22/24) * (3/24)^Z * ..... * (1/24) * (24/24)^W

Where X+Y+Z +... + W=78

Which can be then expressed:

P=(24!/24^102) * (1^X * 2^Y * 3^Z * ....* 24^W)

Now you just need to sum the probabilities of all of the possible sequences for all X,Y,Z...
So I reduced the problem to finding the sum, sorry for notation not sure how to notate this:

[eqn]\sum_{x,y,z...} \prod_{k= x,yln2,zln3...}e^{k}[/eqn]

for all x+y+z+...+w=78

What would happen if a brown dwarf star suddenly gained enough heat in its core to fuse hydrogen? Would it keep fusing as a star or would it not be able to sustain itself?

Is it possible to learn C in 2.5 days

>>8141881
I'm assuming you're looking for a numerical solution by the way the equation is given? How about Newton's method for example?

Can somebody recommend me an analytical Chemistry book ?

Retard here, fucked up my transfer to uni and now I gotta take some higher math courses at CC.

Should I take ODE's and PDE's at the same time? Or just take one? I'm only a little bit retarded so I'll want to take <5 courses just to keep it simple.

>>8142077
You should teach them to yourself on Khan Acadameme and test out.

If I travel near lightspeed, how do I perceive time?

Would it be as if everything moves much faster around me?

>>8141998

I just want to solve for M. I dont know how to re arrange the equation in a way that I can finally optain M like the author always does (without going step by step).

File: solveforM2.png (16KB, 330x151px) Image search: [Google]

16KB, 330x151px

>>8142083

Hes another example on a different problem. Same equation. Still, need to do something to it in order to only have M and get its solution.

>>8142095
The original equation you posted leads to a sixth order polynomial equation, and I don't think there's any simple method for solving it analytically. I'm assuming you understand the difference between analytical and numerical solutions. I solved the equation you posted previously with Newton's method and the solution to 2 decimal places I got was 1,96 not 2,00 btw.

>>8142095
as others have said, you really can't solve this for M anon. Your best bet is to type it into Wolfram alpha and ask it to find the solutions. Wolfram will do it numerically, without actually writing it as M = something first.

https://www.wolframalpha.com/input/?i=solve+(4.0178+M)+%3D+((1%2B.2+M%5E2)%2F1.2)%5E3

File: 1424903297925.jpg (2KB, 56x58px) Image search: [Google]

2KB, 56x58px

>>8137349
DUDE WHAT IF ATOMS ARE THE 4TH DIMENSION AND THE 4TH DIMENSION CREATES OUR DIMENSION

>>8142279
kek
niggr

>>8142279
Parentheses are used to denote areas that you do first. They are like their own little problems.
So first you do 2^2 is 4, then5 is 5, so 4pi*4 = 8pi *5 = 40pi

>>8142279
but yeah you need to ask your teacher for help kiddo

>>8142279
roughly 16*15

How do donut shops place all the jelly inside the donut?

Going through a proof book. One of the questions was:
a. find a factor of 2^15 - 1 = 32,767 answer: 31
b. find a factor of 2^32,767 - 1 answer: 2^31 - 1

Can someone explain how you get b? I feel like a retard.

>>8142383
i work at dunkin donuts, and we bake our own.
We have an industrial machine with two hollow prongs that protrude from a box at a length of about 5 inches. A removable tank holds filling, of which we have several tanks and fillings. The machine is programmed for imperial ounces, with 1/2 going into munchkins, and 2 going into donuts. one donut is placed onto either prong, one at a time, and a button is depressed with the right knuckle of the user so that they can still hold the donuts in place. The machine pumps the filling into the donut with a similar mechanism to the spray bottle, and when the gears stop whirring the deafening silence reminds the user to remove the donuts. For croissant donuts, we have an attachment that splits the single opening of the hollow metal prong into 4 openings, so if two of these were used, you could fill 2 croissant donuts which have 4 openings per donuts, or 8 munchkins or donuts with one opening each.

>>8141469
Idk if this method is valid but
order doesn't matter since you don't replace, so you have to make sure to get all 23 items so to get those you need to multiply 24*23*22......2, not one since that would end up picking all 24(not that it makes a difference)
then after that it doesn't matter which one you choose so long as you don't choose the 24th one so (24-1) is your choices for the last things
c=items, p = times picking the items I got this equation :
[eqn]\frac{c!(c-1)^{p-(c-1)}}{c^p}[/eqn]
I got this:
3.869x10^-10

Trying to wrap my mind around prime ideals of rings.

The definition I have is: an ideal P of a ring R is prime iff for all a,b in R, if ab is in P then a is in P or b is in P, and P is a proper subset of R.

I understand why it must be a proper subset; a prime number cannot be equal to 1, and using the the set of integers Z as an example, the ideal 1*Z = Z.

I think my confusion stems from how they defined prime numbers. The definition I'm used to is: a natural number p is prime iff for all x in Z, x|p implies x=1 or x = p. The definition i'm getting from the book (i think) can be written as: for all a,b in Z, p|ab implies p|a or p|b.

>>8142418
>i work at dunkin donuts

I stop reading there, I need proofs. I can't believe you if you don't give the necessary proofs.

>>8142458
Think about it this way.

Consider [math]\left\langle p \right\rangle \triangleleft \mathbb{Z}[/math]

We say [math]\left\langle p \right\rangle [/math] is prime iff for all [math]ab \in \left\langle p \right\rangle [/math] then [math]a \in \left\langle p \right\rangle [/math] or [math]b \in \left\langle p \right\rangle [/math].

By definition, [math] \left\langle p \right\rangle = \left\{ {np\;|\;n \in \mathbb{Z}} \right\} [/math].

So the only way the condition for the ideal [math]\left\langle p \right\rangle [/math] to be prime is if [math]p[/math] is a prime number in the usual sense.

File: ntproof.png (24KB, 378x210px) Image search: [Google]

24KB, 378x210px

>>8142414
try this:
claim: if d divides n, then a^d - 1 divides a^n - 1
proof:
suppose d divides n, then we can write n = dr for d, r in Z. then pic related, and so a^d - 1 divides a^n -1
now apply that to those numbers.

>>8142458
>for all a,b in Z, p|ab implies p|a or p|b.

Yes, it's amusing that what everyone thinks "prime" means isn't really what it means more generally in math. It's equivalent for Z though.

>>8142458
You are absolutely right, it is not a tautological fact that the two properties should be equivalent (actually, it's false in general). The first property you mention (the only divisors up to multiplication by an invertible element are 1 and p) is that of being an irreducible element, whereas the second one (<p> is a prime ideal) is that of being a prime. While a prime is necessarily irreducible, an irreducible element is not a prime in general.
For example, in [math]Z[\sqrt{-5}][/math], 2 is irreducible but we have [math]2 | (1-\sqrt{-5})(1+\sqrt{-5})[/math] although 2 does not divise either factor. Hence 2 is not prime in that ring.
That being said, for unique factorization domains (e.g. Z, K[X], etc), the two definitions coincide.

What's some good electronic science book for beginner ?

>>8141469
http://math.stackexchange.com/questions/58753/unique-ways-to-keep-n-balls-into-k-boxes

File: Untitled.png (13KB, 535x118px) Image search: [Google]

13KB, 535x118px

What does this mean?

File: clipscreen-twBd.png (37KB, 752x125px) Image search: [Google]

37KB, 752x125px

I've been following successfully until this paragraph.

I know that
[math]e^{i \omega (t - xc)} = \cos{\omega (t - xc)} + i \sin{\omega (t - xc)}[/math]
and that I should ignore the imaginary part.

Why it is not
[math]e^{i \omega (x - ct)}[/math]
?

This is from Feynman's Lectures, 1st book, Chapter 49.

>>8142709
There's `divide` symbol missing between all x and c in the first equation.

>>8142705
>>8142705
your approximating the "curve" of those functions around x=0. Using Taylor series
this is the general equation
f(x) is your function ex) e^x, cos(6x)
[eqn]f(a)(x-a)+\frac{f(a)'}{2!}(x-a)^2+\frac{f(a)''}{3!}(x-a)^3...[/eqn]
but since a = 0
[eqn]f(0)(x)+\frac{f(0)'}{2!}(x)^2+\frac{f(0)''}{3!}(x)^3...[/eqn]

Hey guys, simple question. I have a problem with the thought behind a simple equation.[math](h+0.25h^2)/h = 1+0.25h[/math]
I don't understand where the "1" comes from.

What is the cardinality of the set containing all propositions undecidable in ZFC? By a proposition I mean a well founded statement in the language of ZFC and by undecidable I mean undecidable.
I don't have the best understanding of the concept, but I was thinking about it and was wondering if such a set was even well founded. Like could you possibly run into a situation where you'd have to introduce the concept of a class because the set of such propositions is 'too large', violating the axiom of regularity?

>>8142742
h/h = 1

>>8142746
of course, thank you mate

>>8142008
>Chemi
Quantitative Chemical Analysis by Harris

Couldn't recommend it enough

is the hyperreal number ω/2 (or ω/x where x>1) less than a given real number?

I really need help here, it's for my vidya game:

integer1 * constant * 2/3 = anyinteger
integer1 * constant * 4/3 = anyinteger

Additionally, the constant needs to be close to 0.7(reciprocal of sqrt of 2) and integer1 needs to be around like 15. (allot of leeway for both)

Sorry if it isn't possible.

>>8141469
If you have m items and take items out n times then the probability that you haven't seen every single item is
[math]1 - {n \brace m} \frac{m!}{m^n} [/math]
where [math]{n \brace m}[/math] is a Stirling number of the 2nd kind.
I worked it out for the m=4 case (as a Markov chain/transition matrix problem) and just substituted 4's with m's. m!/m^m is the probability of selecting all m items after exactly m items have been taken out but to be honest I'm not sure the meaning behind the Stirling number. I guess from this question {n,m} m! must be the number of ways to select n items from m with repeats such that none of them are left out.
Plugging in your values the answer is ~0.276322.

>>8142933
integer = 0, constant = 0

>>8142866
positive real number, yeah

>>8142933
>>8142937
It's for a vidya game sci cuck and you didn't even listen to the criteria

Anyways I solved it while you neckbeard fucks fingered your bunghole before using the same digit to take nutella out of the family nutella thing. SUCK IT

>>8142945
That was an unnecessarily hurtful thing to say

>>8142963
Sorry. So I have this now:

trueCameraY -= speed * 0.7 * 2/3;
trueCameraX -= speed * 0.7 * 4/3;

My game is isometric, so the camera moves twice as far horizontally as it does vertically when travelling diagonally (it moves by speed when going straight up or to the right)

Is it wrong to use 0.707 here to weaken the two components of the overall movement vector? If so how can I find the number I should use?

>>8142709
>>8142711

one reason you know it can't have terms like: wx, wct is because of units. the exponential function can't have any units in the power so that can't be a physical answer.

not sure if I can give a good explanation for the real reason but the results he gives are general forms for waves as functions of position and time.

>be me
>need to self-study Physics because I am gonna take it for the first time
>always get bored watching the videos
>don't even have the motivation to open the book to do the reading and work on the problems

What can I do, /sci/?

why the fuck do people use d / dx notation?
[variable name] prime makes more sense
anyways, why do you always multiply every derivative of y by y' in implicit differentiation

>>8143066
You're fucked m8.

File: 1465977353923.png (133KB, 487x622px) Image search: [Google]

133KB, 487x622px

What actually happens when a material "slows down" light?

>>8143373
refraction

File: josh proof.png (11KB, 600x463px) Image search: [Google]

11KB, 600x463px

Is there someone kind enough to decipher this fucking mess of a "proof?"

>>8143395
2 + 2 = 2 / 2 = 4 = 1

>>8143393
What actually happens when a material "slows down"/refracts light?

also
>"(you)" didn't show up after the post number

how is space similar to a leaf?

how is time real and not just a social construct

>>8143395
>>8143396
Isn't that an infamous Common Core question?

>>8143404
No. It's from an idiot.

>>8143407
Also he used it to disprove relativity.

>>8143167
>why the fuck do people use d / dx notation?
It's an absolute necessity when you have multiple variables. It may be obvious that y' is with respect to x when you're just doing y = f(x), but if you have z = f(x, y) or any other number of variables, it's no longer obvious which variable you're differentiating in respect to, and you could have instances of each one depending on what you're doing.
Also it's just more versatile or easily understood in that you can say d/dx (big long expression) and it wouldn't make much sense to say (big long expression)'. Is that a 1? Is it an apostrophe? Just less confusing.

>why do you always multiply every derivative of y by y' in implicit differentiation
y' is the derivative of y. I suppose you mean why you multiply every derivative of a function of y by y'. Like if you have something 2y^2 you get the derivative as 4y dy/dx ? This is just the chain rule. df(g(x))/dx = f'(g(x))g'(x). In the previous example you have a function of y, which is a function of x.

I'm starting my physics major (CS minor) in October, and have the next 4 months free. I plan on using them mostly for preparing, but am at a lost for direction.
In what direction should I be looking at in regards to books/subjects to focus on/etc?

>>8143422
Make sure you are comfortable with all the Calculus (up through multi variable things, Stoke's theorem, etc.), linear algebra, and differential equations.

>>8143395
5+8=10
8=4+4
4=2+2
2/2=1
therefore 8=4+1 and 5+8=10

File: image.png (351KB, 500x334px) Image search: [Google]

351KB, 500x334px

How much truth is there behind "genetic" obesity?

>>8143413
If you have a function of multiple variables, you're not taking a total derivative with respect to a single variable.

>>8143756
>http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3137002/

even with good genetics, the household you grow in influences you a lot.
I remember my parents letting me and my brother eat as much as them, if not more on a regular basis, treating kids in their early teens as adults in terms of food. I still resent them for that.
Was not obese, but not far.

File: Mom2.png (3MB, 1409x1593px) Image search: [Google]

3MB, 1409x1593px

Anybody knows about Compressible Flows here?

I am going to have an exam and I know for a fact that the teacher is going to ask something I dont have much idea on how to answer.

Its something along the lines ''Find the optimal ratio of divergence to expand Air from standard conditions to a certain pressure, using a convergent - divergent nozzle''

So I know that Stagnant Conditions will be the Standard Conditions (Po, To) and the pressure they wish to expand this fluid to (much lower obviously) would be P2. Right?

But what do they mean by ''Ratio of Divergence''

I am fucking dumb please help

>>8143924
sauce on pic pls :3

>>8143927

I dont remember who exactly, since that pic is everything there is about it.

It was either Rojiura Jack or Marumiya. Both of them lots of their shit on ge hentai.

>>8143935
k thx. apparently its marumiya

>>8143613
Thanks. Anything when it comes to CS? I haven't taken any programming classes in high school.

File: Screenshot from 2016-06-15 12-00-34.png (14KB, 621x177px) Image search: [Google]

14KB, 621x177px

Anyone have any hints for the two in pic related?

File: 6.jpg (29KB, 800x452px) Image search: [Google]

29KB, 800x452px

How would you solve this only using add sub divide multiply.

>>8144037
it's been a while but isnt for 6, the fact that nullity + rank = 5 imply that if null is either 0,1,2,3,4,5 then rank is 5,4,3,2,1,0, respectively, so you can't have same nullity and rank hence the result

>>8144068
That sounds right, thank you! I suppose for the first then that I need range T and null T to both have dimension 2...

>>8137940
arcsin is an inverse function of the sine function. For example, arcsin(1)=π/2 , 5π/2 , 7π/2 etc.

However, csc(x)=1/sin(x). So, csc(π/2)=1. arcsin is used for solving something in the form sin(x)=b whereas csc is used to describe the sine of a function in a different way. It is particularly useful in evaluating integrals.

>>8144077
And now I've got the first one,
[math]T(x_1, x_2, x_3, x_4) = (0, 0, x_1, x_2)[/math]. Then [math]\text{null }T = \{(0, 0, x_3, x_4) \mid x_3, x_4 \in \mathbf{R}\} = \text{range }T[/math].

>>8144080
> csc is used to describe the sine of a function in a different way
Specifically:

sin(a) = opposite / hypotenuse
csc(a) = hypotenuse / opposite

cos(a) = adjacent / hypotenuse
sec(a) = hypotenuse / adjacent

tan(a) = opposite / adjacent
cot(a) = adjacent / opposite

>>8137940
Different meanings of ^-1 (both of which may be called the "inverse").

f^-1(x) means the inverse of the function, i.e. if f(x)=y then y=f^-1(x). f(f^-1(x))=f^-1(f(x)) = x.

(f(x))^-1 means the reciprocal of the function's value, i.e. 1/f(x). The reciprocal is also called the multiplicative inverse or sometimes just "inverse", but reciprocal is preferable as it is more specific and avoids confusion.

arcsin() is the inverse of sin(). The cosecant (csc) is the reciprocal of the sine (sin).

File: Article%20Lead%20-%20wide1001139054gk1vyuimage.related.articleLeadwide.729x410.gk1vu6.png1444291527054.jpg-620x349[1].jpg (58KB, 620x349px) Image search: [Google]

58KB, 620x349px

In The Martian, he blows up the Hab. Losing his plants, the soil microbes, and a lot of his water. Yet he still had his current dirty potatoes, he is still pooping, and he still had some water and hydrazine.

So why didn't he just start over?

He started from sterile Martian dirt, some vacuum packed potatoes, and hydrazine. So restarting wouldn't have been as difficult, since he wouldn't be starting from Zero like last time.

>>8143861
Thank you for answering.

>>8144089
You might want to rethink that.

>>8140474
Bumping this question and also throwing in

How do I take a quotient of the standard 3-simplex to get a complex on S3? I visualize S3 as an S1 bundle over S2, and the 3-simplex is topologically D3, so I'm trying to identify the faces in a way that makes sense in terms of giving me some sort of space that looks like an S1 bundle over S2.

Show if: hof=fok, then h=k is not true in all cases even if f has an inverse.

Book recommends finding a counter-example involving one set, three endomaps of that set and endomaps f, h, k of a two-element set A with f invertible and hok = fok but h=/=k.

I've tried several possibilities and cannot figure out how to show this.

>>8144445
If S = {a,b,} and f(a) = b and f(b) = a, let h map all of S to a, and let k map all of S to b.

fok(a,b)=f(b)=a
hof(a,b)=h(S)=a

but k =! h

I think this is what you want.

Any gentoomen know if I can add a virtual adapter to a bridge?
[code]ifconfig eth0:0 192.168.0.1
brctl addif br0 eth0:0[/code]
I don't want to kill the only connection I have to this server.

>>8144470
Thank you, that is clever.

How did you come up with the example so easily?

The trick here is that while f is invertible, h,k need not be it seems.

>>8144613
I'm a maths student so part of it is probably just experience. The fact that f is invertable on a two element set implies f is either the identity or the interchanging of the two elements.

Bijections on a two element set commute, so if h or k was bijective, we would have
hof = fok = kof and then by cancellation of f we have h = k

So h and k must be distinct nonbijective functions which means one must map all to A and one must map all to B

>>8142866
No. If it were less than x, then ω would be less than 2x

I'm reviewing some algebraic topology for quals, and I'm having a hard time proving that paths lift to covering spaces. Here is my issue and my thoughts.

Let [math]p : \tilde X \to X[/math] be a covering space and [math]f : I \to X[/math] a path in X. Then for each [math]t \in I[/math], there is a neighborhood [math]U_t[/math] of [math]F(t)[/math] which is evenly covered (i.e. its preimage under p is a disjoint union of open sets mapping down homeomorphically). We then cover [math]I[/math] by the preimages of these open sets and use compactness and some nonsense to say that we can partition the unit interval into open sets [math](t_i,t_{i+1})[/math] such that [math]f((t_i,t_{i+1}))[/math] is contained in an evenly covered open set. This is almost exactly what we need, because we can define the lift using the local inverse of p, but I think somehow the endpoints of the intervals need to be contained in these evenly covered sets as well in order to extend the lift from interval to interval. How can I show this is true?

File: chemex-8-cup-classic.jpg (704KB, 1800x1800px) Image search: [Google]

704KB, 1800x1800px

I'm thinking about getting something like a chemex brewer for coffee, but I'd much rather get something I can also use for general chemistry.

any ideas senpai?

>>8136206

Here's my stupid question. How do you math print like that?

>>8144858

I wouldn't use sometime for coffee and something for experiments...cause you know, you might die.

>>8144881
I'd keep track of what I used it for last though anon. Is it really a shitty idea?

>>8144858
You haven't been in chemistry very long have you? This is not advised.

>>8144885
Not him, but yes, incredibly shitty. You don't want to put food through something that you could potentially have run hazardous reactions through. No matter how clean you get it, there will always be a little bit of leftover residue that could be hazardous to your health.

can time be a physical dimension that we just can't perceive? aka the past the present and the future are just there on a space.. i guess. probably sounds like i'm high but i just suck and this is stupid questions thread anyway.

>>8140855
original anon here...

https://www.youtube.com/watch?v=wZzHnZzm_58

In the event there's anyone out there.

>>8135617
What's the proof for raising both sides of an inequality by 'n'? Like if x<y, that how do you prove x^n < y^n?

>>8145008
First it's not true in general, only for 0<x<y

Use 0<a<b and 0<c<d implies 0<ac<bd and induction to get the general n

Let me know if you need more help.

>>8145014
Nah that makes sense, thanks man.

I recently bought a pair of 100Ah 12v batteries for a festival sound system, but was wondering how low I can drain them. The guy in the store said I can drain them all the way but I've read about 80%, so what is it? Is the 100Ah rating the total cap or the 80% level? In other words will i get closer to 100 or ~80Ah out of them before having to recharge? I won't ruin them by discharging too much as they have an indicator light. They're AGM batteries btw.

>>8145050
What voltage do you want? Most batteries go above their nominal voltage for their nominal capacity. Your voltage will start above 12, will probably end below 12 by the time you'd get to 100Ah. Batteries that large would be lead acid, and you don't want to over-drain them. The more extreme you drain them the fast they decay. If you want, just slap on a voltmeter, and see how much you have to go down from a full charge to reach either 12.0V or 100Ah, whichever comes first. If you know your power output (either an ammeter, wattmeter, or a consistent and verified load like light bulbd) then you can get an Ah estimate from that.

>>8144050
I am checking those quints. no ban pls I am saging

>>8145062
I mean the amplifiers I'm using aren't so sensitive to voltage as they run on anything between 18-40v but the batteries are in series for 24-25v. I just wanna get as much juice from the batteries as possible before having to charge. Maybe I'll do the voltmeter thing

>>8145072
Having to charge and not damage the batteries*

>>8144887
no I just do a lot of mycological work and some synthesis, thought it'd be fun to synthesize my own coffee in a chemistry sorta way. purely out of hobby

>>8145072
Yeah then you might want to see what voltages you can get.

http://electronics.stackexchange.com/questions/177032/how-bad-is-it-to-undervoltage-a-12-volt-lead-acid-battery

Read the first response. He's got some numbers.

>>8145122
Alright thanks

File: 1425511501951.png (151KB, 870x345px) Image search: [Google]

151KB, 870x345px

I'm having trouble understanding vapor pressure of a solid. Why is it independent of the volume of its container?

Why is it independent of other pressures in the container?

What happens once all the material is evaporated? i.e. if the temperature keeps rising. Do the molecules in gaseous phase keep moving faster resulting in higher pressure which follows the vapor pressure curve?

This is more of a general question than a /sci/ question, but whatever.

So recently I've been drinking, not so much that I don't know what I'm doing but so much where I can see how often I mispell things and correct them before I post them.

It has hit me in this somewhat inebriated state that I can still perform basic computations and whatnot. I have thus come to the hypothesis that one way to conclude whether or not you really know something is to do so while somewhat intoxicated. If you can perform the activity, then you clearly know how to do it. If not, then you should study more. Is this a reasonable claim?

For example, if I know how to solve a problem requiring the use of an inverse trig identity while slightly drunk, can I conclude that I know it well enough to remember sober?

>>8145220
You can search up on the "ballmer peak" for more information

Can someone link me to that tumblr with all the advanced biochemistry humor that nobody gets?

>>8144110
>arcsin() is the inverse of sin(). The cosecant (csc) is the reciprocal of the sine (sin).

OK thanks, I get it now

>The reciprocal is also called...sometimes just "inverse", but reciprocal is preferable as it is more specific and avoids confusion.

That was the source of my confusion.

>>8144668
Well you're almost done, you just need to refine the nonsense a little bit to say that you can choose intervals of the form (t_i,t'_i) with t_i < t_{i+1} < t'_i. It's just a matter of waving your hands at this point, all the important ideas are there.

>>8137462
Ignore the math fags bitching about Notation. Just see it as Delta x with the smallest Delta possible. Also makes seperation off variables much more straightforward, and its possible to handwave proper justification for it.

What is the importance of going to a "good" university?
I ask this because a shorter commute time would reduce stress and increase free time.

>>8145470
You can think of it as whatever the fuck you want, but he asked what it means. It has no meaning in Riemann integration beyond notating the variable of integration in multivariable calculus.

>>8144634
Thanks man! Excellent explanations.

>>8137462
It's a differential. It's like saying, "I have one part of a slope", which only gains meaning when it's paired in ratio with another differential, or when used as a driver to tell the integral where to go.

>>8135840
Unless you're talking about Polya theory. Do rotations around the table matter?

>>8145487
This would be my answer too, but maybe only because I want to avoid some discussion that will be filled with vague arguments. The fact though is that it's there because there is a \Delta x in the sum before the limit is taken, and was thought of as a kind of infinitely small change in the limit.

>>8145478
The last school you go to should be the best you can get into. If you are doing more school after, i.e. grad school, where you go now won't make that much difference.

>>8144668
Can you start with the collection Z of all evenly covered local neighborhoods in X (before even considering the path) then looking at the collection {z in Z | f^{-1}(z)} ? Won't this be an open cover of I?

What do you get when you are done? It's not really a path, because your path function is one-to-many. And if that's the case, why not just define the path as p^{-1}(f(t))?

Genuine curiosity... I don't know this stuff very well.

>>8136395
>>8137829
>>8136395
>>8137829
biotech startups are popular in a few hubs throughout the US - Raleigh, NC and Boston, MA among them. had a friend move to Boston recently to work at a startup only to get laid off 3 weeks later because they lost funding.

>>8145879
So the idea is that globally you have no clue how to lift a path. For instance, even within one of the evenly covered neighborhoods you don't have an inverse for p until you pick a sheet of your cover. However, when you partition the interval, you can define the lift piece by piece inductively on each section after you pick any starting point in the fiber over f(0). Since you know where the last section of the lift ended, you know which sheet you should pick for p^{-1}.

Try working through drawing a lift for the reals covering S^1 using this method. The proof works by basically telling you where to go next -- you just keep going where the line is already drawn!

>>8145390
The ballmer peak just says that you can perform better with a light buzz, I'm talking about actually getting a little drunk and then testing what you remember. So I guess I'm talking about going past the ballmer peak to the point where the negatives outweigh the positives and seeing what you can do then.

>>8139130
you're stupid as shit

>>8145926
I think I see.... so if you have a path f(t) = exp( 4 pi i t) on the circle, and p(s) = exp( 2 pi i s), then the lifted path would be {\tilde p}(t) = 2 t ?

>>8143413
ok, I kind of understand
what about dx / dx, what does that mean?

>>8144000
cs is a shit show, being saturated by code monkeys
look at the market saturation now, it will be quadruple in 4 years
what you're most likely going to get is some code monkey job writing java
I suggest you start with that.
If you really want to know more, learn C, assembly, and algorithms

Okay...

So when light from distant galaxies finally reaches us, it has become redshifted. It has lost energy (has a longer period).
But how can light, say from the Andromeda galaxy, become blue shifted? Does it gain energy on its way over here??

>Kip
>A fucking kip
>A unit of measurement for force
>lbf was not enough
>lbf because just lb is mass
>the imperial system
Jesus Christ what the fuck is wrong with these people. Kill yourself if you use these units. Luckily I don' t have to use them but just knowing they exist makes me so fucking mad.

I don' t have a question.

anybody here doing a double major that ISN'T in math/physics?

>>8146548
I plan on trying to get a job in the field, CS seemed like the most logical minor to choose.
Is there a better minor to take with my physics major in order to get a job related to the field? Or does the minor not matter as much getting a M.Sc./PhD?

If quantum tunneling of photon is FTL, how come it does not violate principle of causality?

File: bt2lf0615_a.jpg (144KB, 656x439px) Image search: [Google]

144KB, 656x439px

>>8146556
Like sound gets higher when it approaches you. Its denser.
More oscillations per same timeperiod, more excitations of the molecules it hits on same timeframe.

>>8146556
>>8146684
Also the redshifted light didn't lose any energy over distance, it loses nothing.
The redshift is due to the source moving away, which results in less excitations per minute from your perspective, shifting it towards the lower energy red spectrum.

>>8146597
Elec eng/commerce

File: 2016-06-17-015614_267x182_scrot.png (8KB, 267x182px) Image search: [Google]

8KB, 267x182px

How would I show that in this circuit [math]\frac{ \Delta R}{4R} = \frac{\Delta U}{U}[/math] when R = R2 = R3 = R4 and you change the resistance of R a small amount?

>>8139123
>a^b+c = a^b * a^c
a^(b+c) = a^b * a^c

Every tick:

trueCameraY -= speed * 0.7 * 2/3;
trueCameraX -= speed * 0.7 * 4/3;

My game is isometric, so the camera moves twice as far horizontally as it does vertically when travelling diagonally (it moves by speed when going straight up or to the right)

Is it wrong to use 0.707 here to weaken the two components of the overall movement vector? If so how can I find the number I should use?

>>8144668
use this?

https://en.wikipedia.org/wiki/Lebesgue%27s_number_lemma

take cover, get delta, make tiny overlapping intervals?

I've got a practical question about electricity. My computer has a power source of 600W, and I'm gonna use it with a no-break of 450VA. I have a rough understanding of this stuff (barely), but it's not enough to know if my computer will work with said no-break. Anybody knows about this?

>>8147570
no
450<600

>>8146691
are you taking them both simultaneously? how hard is it? i guess more importantly, is it worth it?

>>8146691
aurais-je trouvé un supelec/escp?

>interested in how method used by one group works
>paper is in a journal my uni doesn't have access to
>request paper via interlibrary loan
>get PDF four days later
>the "Methods" section just says "Methods and any associated references are available in the online version of the paper."

Why is this shit allowed?

File: funct.jpg (3KB, 154x73px) Image search: [Google]

3KB, 154x73px

I need to approximate this function at point 1 to 0,001.

How do I go about this?
I figred it's f(1) = 1/e but what then?

>>8147960
e is approximately 2.7182718. Plug that in.

>>8147960
how good of an approximation do you need? just take the slope at the midpoint and make a line

so f(x) = x/e. But that's a really shitty and not much easier to calculate approx

>>8148121
I need to calculate the approximate value to 0.001 of this function at x = 1 (I assume, it said at point 1).
I know the approx. value of e but this is Calc 2 so I'm guessing it has to be done in some way I'm not aware of.

File: Untitled.jpg (58KB, 800x600px) Image search: [Google]

58KB, 800x600px

Explain this.
How one wave can be in 3 places simultaneously?

>>8148179
If it's calc 2 I'm guessing it has to be done via series approximations. Just plug -1 into the maclaurin series for e^x and add as many terms as you need for accuracy.

>>8148188
I plugged it into the maclaurin and it just gives me
1-1+1-1+1-1.....
I can't wrap my head around the solution for this.

>>8148221
scratch that I'm just an idiot

>>8148188
Alright I did for n = 6 and I have a value and what then? There's still the x^2 in the function and I just got some e values. If at point 1 do I just assume it's the approximated e value times (1) squared since I'm approxing it at x=1?

How do I prove if both x and y both are not zero, then x^2 + xy +y^2 is greater than zero. Sorry, I know I'm an idiot but I need help with proofs. Also, can someone hint to me how to then prove x^4 + x^3y + x^2y^2 + xy^3 + y^4 > 0? Spivak is making me feel retarded, and I'm not even up to the calculus.

>>8148187
because it is not focused, as drawn, but propagates in a cone

>>8148553
x^2 + xy +y^2 = (x+y/2)^2 + 3/4 * y^2

always try to complete the square
too lazy for the other one

Starting out with Simulink. Is there a block that sends a continuous signal (like a probability density function) upon receiving a discrete signal (like a Dirac-impulse)?
I can't use the convolution, like I would've liked to do. :/

>>8148553

Putting

x^4 + x^3 y + x^2 y^2 + x y^3 + y^4 where y=w+z and x = w-z

into Wolfram alpha gives

5 w^4+10 w^2 z^2+z^4

which is clearly positive

Why is rolling friction always smaller than sliding friction?

>>8148553
One more way (I think I saw this in Little Spivak):

x^2 + y^2 > (max( |x|, |y| ))^2 >= - xy

And

1. x^4 + y^4 > (max( |x|, |y| ))^4 >= max( -xy^3, -yx^3 )

2. x^2y^2 >= min( -xy^3, -yx^3 )

Add 1 and 2 to get your inequality

You could also note that
x^2 + xy + y^2 = y^2*(1 - u^3)/(1 - u)

where u = x/y, and it is assumed that x != y
Now just consider the cases u > 1 and u < 1 separately. You can do a similar thing for the second inequality.

When calculating trusses and their internal forces, is there a way to know if my results are correct? and if there is, how?

Lin Alg 101 here. Exactly why does the cross product between two vectors (A×B) result in a vector that is perpendicular to both? Is it magic?

Which is better (Waterloo by the way)? ChemE or Double Degree in Math and Business Management?
I'd imagine Math gives you knowledge gains and also double degrees get you set for a job, but ChemE pays more, I believe.

>>8149297
Maybe you could argue that it produces a number which is not part of the original numbers, but is logically defined. i cross k and j cross i are dimensional operators that would either be commutative or not (this exercise is left to the reader), i cross j can be defined as a unique entity related to, but cannot be defined to exist along in the previous dimensions, so the new dimension is k. Similar to the square root of -1.

>>8149413
i cross j and j cross i*

>>8148553
[math]x^2 + x y + y^2 = \frac{1}{2} ((x+y)^2 + x^2 + y^2)[/math]
[math]x^4 + x^3 y + x^2 y^2 + x y^3 + y^4 = \frac{1}{2} ((x+y)^2 (x^2+y^2) + x^4 + y^4)[/math]
Right hand sides are always positive so left hand sides must be also.

Is it possible to make a math map, like one for like relevance and how it pertains to problems? i hope people understand what I mean.

>>8148553
> x^2 + xy +y^2 is greater than zero.
Substitute x=p+q, y=p-q and simplify to get
q^2 + 3*p^2

> x^4 + x^3y + x^2y^2 + xy^3 + y^4 > 0
Substitute x=p+q, y=p-q and simplify to get
q^4 + 10*p^2*q^2 + 5*p^4

Is there a reason that my internet downloading speed would drastically increase to over twice as much as I've ever seen, and stay this way for days?

>>8148576
>>8148635
>>8149210
>>8149446
>>8149724
>all this extra work...

x^n + x^(n-1) y + ... + x y^(n-1) + y^n = (x^(n+1)-y^(n+1))/(x-y)

Top and bottom always have same sign, so whole thing is positive.

>>8149812
you got a free upgrade.

>>8149828
what if x=y?

>>8149812
It's common for FBI to raise its target bandwidth before they execute the arrest, so they can gather more incriminating evidence of downloading cp, pirated software, etc.

Let G have order p^n m where p is a prime and p does not divide m. Suppose that m < 2p. Show that G has a normal subgroup of order p^{n-1} or p^n.

>>8149297
I don't understand the question. The cross product isn't some operation sitting out in nature that we captured one day and are trying to understand. We wanted an operation which would make a vector perpendicular to it's input, so we made one

>>8149297
It is stylistically designed that way

>>8149297
The cross product is simply the vector X such that X.A=0 and X.B=0. Write out the equations and solve them for X, and you'll get the cross product.

Because these equations are homogeneous, the solution is only unique up to a scale factor (i.e. if X is a solution then so is k*X for any scalar k), which is why you only need two equations for 3 variables.

Also:

The cross product is one row of the matrix of cofactors formed from A, B and any other vector.

By Cramer's rule, the dot product between one row of a matrix and a different row of the cofactor matrix is zero, i.e. the two vectors are perpendicular.

You can use this fact to generalise the cross product to any number of dimensions. In N dimensions, you need N-1 vectors in order for the perpendicular to be uniquely determined (up to a scale factor).

https://www.youtube.com/watch?v=PWsg0OtCZgQ

In this video, he says that the conjugate of P(a) is equal to the conjugate of 0 if P(a) = 0.

How is this true? Wouldn't that mean that 2 - 3 = 5 - 0?

Does these conjugate rules hold if one of the "sides" are non-real complex?

What's the difference between technique and technology? If you're not a native English speaker please notice, that in your language the definition of both are probably switched.
Some examples, preferably using CS terminology, would be appreciated.

Betrands postulate (theorem) states that there is always a prime between n and 2n. Legendre's conjecture is that there is always a prime between n^2 and (n+1)^2. The difference between adjacent squares is 2n +1. Since this is clearly bigger than n, why isn't Legendre's a corollary of Bertrand? I know I'm being a brainlet, but SQT.

>>8149941
That's actually kind of mildly worrisome since I accidentally one of those "this page has been taken down by the FBI!" sites a few days ago but I think the internet thing started a couple days before that maybe. Who knows. No sense in falling into paranoia.