SQT - Stupid Questions Thread

[Anonymous No.7918315]

Questions that don't deserve their own thread. I'll start us off.

Lads, I'm plebing out here.

Using:

[eqn] \frac{1}{1-x} = \sum_{i=0}^{\infty} x^{i}, |x| < 1 [/eqn]

Find a power series for:

[eqn]f(x) = \frac{1}{(1-3x)^{2}} [/eqn]

I know the derivative 1/(1-x) gives me 1/(1-x)^2. But what's the correct way to manipulate 1/(1-3x)^2 ? Runnin on 36 hours no sleep lads, the assignment is due soon.

[Anonymous No.7918318]

Nice attempt in disgusing a homework thread as a stupid questions thread.

[Anonymous No.7918326]

>>7918318

:^) thanks m8, I tried.

[Anonymous No.7918385]

>>7918315


If I'm not mistaken you can take the derivative of the power series and then replace the value of x with 3x. If this doesn't work, then definitely think about manipulating the power series as opposed to the original equation, as that's easier to manipulate from what I remember.

[Anonymous No.7918389]

>>7918385
This

[Anonymous No.7918400]

>>7918315
help

[Anonymous No.7918453]

Wait I have a stupid cosmology question. They say the expansion is accelerating. So is it expanding faster now than when it first started? I thought there was a period of inflation. Are these two terms different?

[Anonymous No.7918467]

>>7918315
derivate then evaluate when x=3x

[Anonymous No.7918712]

Why don't schools just teach maths like linear algebra, calculus, etc.. using set theory instead of teaching students to plug and chug?

[Anonymous No.7918723]

What is the most commonly used/important statistical tests in physics (p-tests, t-tests, z-tests, etc.)?

[Anonymous No.7918750]

Why are definitions of vector addition/ scalar multiplication other than the standard definition allowed? Does it have something to do with vector spaces being "stretched" or "distorted"?

[Anonymous No.7918755]

>>7918750
What the hell do you mean with the standard definition?

[Anonymous No.7918765]

>>7918755
real number addition/multiplication?

[Anonymous No.7918774]

>>7918712
because some students don't even comprehend the latter and don't even want to comprehend it. they're glad if the whole thing of mathematics is finally over and they get a D so they can pursue the things they really enjoy and which are completely disjoint to numbers and functions

[Anonymous No.7918776]

>>7918765
Polynomial multiplication?

[Anonymous No.7918783]

>>7918776
no

x⊕y = x + y
c⊗x = c * x

[Anonymous No.7918818]

When water inside a close container freezes and "blows up"(I don't know the term) the container, where does the energy come from?

[Anonymous No.7918830]

>>7918765
This only works if your vector space is [math] \mathbb{R} [/math]. Usually the vectors aren't real numbers.

[Anonymous No.7918851]

>>7918385
so basically this would be:
1 / (1 - 3x)2 = (sum(i=0, infinite){3^i * x^i})2

[Anonymous No.7918860]

In lagrangian dynamics, what's the logic towards constructing your equation of constraint?

[Anonymous No.7918882]

>>7918860
Take whatever constraint you have, [math]f(q_1, \dot q_1, q_2, \dot q_2)[/math]
Find the differential of it in q's. Separate and get as functions of dq1 and dq2
Substitute each dq in the form of f into the action equation:
[math]\delta S=\int L Dr[/math]
Use minimum variation to receive your Lagrangian with constraints.

[Anonymous No.7918889]

So I've got a similarity on [math]\mathbb{R}^2[/math] which means that [math] | \phi(x) - \phi(y) | = C | x - y | [/math]. How the fuck do I prove that [math] \phi(0) = 0 [/math]?

[Anonymous No.7918891]

>>7918882

that makes sense.

thank you

[Anonymous No.7918987]

We just covered the hydrogen atom using the 3d Schrodinger equation. What if the quantum number 'n' is zero? We're only first year so the lecturer skipped the maths sadly.

[Anonymous No.7919004]

>>7918889
Take phi(x)=x+(1,0).

Then phi(x)-phi(y) = x+(1,0)-y-(1,0)=x-y. Thus |phi(x)-phi(y)|=C|x-y| with C=1. However, phi(0)=(1,0) and not 0.

You're missing something, somewhere.

[Anonymous No.7919080]

>>7918830
their components are usually real/complex numbers, though

[Anonymous No.7919105]

>>7919080
You can always view finite dimensional vector spaces as having coefficients over your field, but it's not always obvious how to see it that way. Many times you might be working vector spaces without any idea as to an explicit basis. Things like the vector space of continuous functions on some manifold don't even have an analogue in the standard addition.

[Anonymous No.7919125]

>>7918818
It's the energy that was binding the molecules of the solid container together. When it breaks those bonds dissapear and the energy turns into kinetic energy/sound/whatever

[Anonymous No.7919157]

Logarithmic function
x --> log(a) x

Now, why in the world can X not be negative? Or rather, why can't it without the result of the function being an absurd value?

Pic related: why is the result mot simply 3?

I feel that I'm missing something

[Anonymous No.7919163]

>>7919157
I should specify that the definition I found states the a has to be a>0 V a=/=1
Why is that?

[Anonymous No.7919170]

>>7919163
Well assuming I understand the question, these functions are not well-behaved when unless a is positive and not 1.

If a = 1, then [math]\log_1(x)[/math] would have no possible value unless x is 1. For negative a, you would get a really nasty function that jumps around and is only even defined in a few places over the reals.

[Anonymous No.7919177]

can you use specific gravity to find the volume of water in a mixture?

specific gravity=ρmixture/ρH2O

ρmixture=(mass1+massunknown)/(volume1+volumeunknown)

[Anonymous No.7919186]

>>7919170
Yeah I know it would be nasty as shit, but it would be a function all the same wouldn't it? Why does this definition specifically require that a>0? I mean you may not want to use the a<0 part all that much for most purposes, but that's no reason for saying it doesn't exist.

[Anonymous No.7919189]

>>7919186
You can give a better definition of negative base logs using complex numbers, which I think is what Wolfram is doing. Look near the beginning of any complex analysis book.

[Anonymous No.7919201]

>>7919189
I've seen some i pop out here and there, but unfortunately I'm not at that level yet

Guess I'll have to wait to figure it out

[Anonymous No.7919203]

>>7919201
I promise it's not hard. You could get up to speed enough to handle complex logarithms in a day -- it's just an application of Euler's formula.

[Anonymous No.7919315]

My linear algebra prof said in my class that polynomials can be vectors, aren't polynomials supposed to be sets of vectors/vector spaces?

Also, how are all matrices considered vectors?

[Anonymous No.7919318]

>>7919315
https://www.youtube.com/watch?v=JpPNzdlXVYw&list=PL01A21B9E302D50C1&index=25

[Anonymous No.7919332]

>>7919315
these are such trivial questions that it would probably benefit you to actually try to work these things out rather than shitposting on /sci/

i'll help you though
try to prove that the set of all polynomials with real coefficients is a vector space

then try to make a vector space out of the set of m by n matrices with real elements, for arbitrary m and n

these are very easy exercises if you know the vector space axioms

[Anonymous No.7919336]

>>7919315
Spell out the definition of a vector space and your question will fade away.

[Anonymous No.7919348]

Manifold learning question: What types of data are appropriate for Isomap, LLE, and Laplacian Eigenmaps?

[Anonymous No.7919352]

>>7919004
You're right! Anyway, is there a way to prove something is a bijection without having to prove its surjectivity?

Surjectivity in the function I just described is a pain in the ass.

[Anonymous No.7919374]

>>7919352
Bijection is defined as injectivity AND surjectivity, so you literally have to prove both.

[Anonymous No.7919385]

back in Secondary High school, my math teacher lamented over how we stopped short of the 1900 in terms of what we were learning, what does one miss that would be so important?

[Anonymous No.7919401]

>>7919385
stats and linear algebra were developed in the 20th century though

[Anonymous No.7919421]

>>7919401
pls help
i know that if you dot the del thing into F you get : \frac{1}{R^{2}} * \frac{\partial }{\partial R} * R^{2} * F_{R} = 1

[Anonymous No.7919425]

>>7919374
I know, but I did something smarter to prove it, instead of proving each similarity [math]\phi[/math] is a bijection, I proved that if [math]\phi[/math] is a similarity, then [math]\frac{ \phi }{ C } [/math] is an isometry. So from that it follows that [math]\phi[/math] itself is also a bijection... right?

[Anonymous No.7919428]

>>7919421
fuck
[math] \frac{1}{R^{2}} * \frac{\partial }{\partial R} * R^{2} * F_{R} = 1 [/math]

[Anonymous No.7919445]

>>7919421
>>7919428
[math]\frac{1}{R^{2}} \frac{\partial }{\partial R} R^{2} F_{R} = 1[/math]
[math] \frac{\partial }{\partial R} R^{2} F_{R} = R^2[/math]
[math] R^{2} F_{R} = \frac13 R^3 + C[/math]
[math] F_{R} = \frac13 R + C/R^2[/math]
Literally just fill it in

[Anonymous No.7919586]

What university is better, CP Pomona or UC Riverside?

[Anonymous No.7919594]

When does a set of vectors not span a vector space?

[Anonymous No.7919598]

My definition of a smooth embedding in differential geometry: smooth immersion which is also a homeomorphism onto its image. I know that a smooth, injective immersion which is also PROPER is an embedding. Does the converse hold ?

[Anonymous No.7919609]

>>7919594
If their span is either smaller or larger than said subspace. More precisely: if there's a vector in the subspace which cannot be written as a linear combination of the vectors in the set OR if there's a linear combination of the vectors in the set which doesn't belong in the subspace. The second case will never happen if you're asking about the whole space and not just some subspace.

[Anonymous No.7919619]

>>7919609
>a vector in the subspace which cannot be written as a linear combination of the vectors in the set
This is what confuses me. How can you even show that a vector cannot be written as a linear combination?

[Anonymous No.7919664]

>>7919619
Every vector can be written as a linear combination of itself.

[Anonymous No.7919670]

>>7919664
I mean as a linear combination of a different vector

[Anonymous No.7919675]

>>7919670
different vectors*

[Anonymous No.7919676]

>>7918453

i'm not really into this, but i think it slowed down in between. now it goes full inflation again.

[Anonymous No.7919680]

I'm using an ARIMA(111)-SARIMA(011) to make predictions.

I have one variable that I want to predict and about 15 independent variables to choose from. What steps should I take to ensure that my predictions are sound, not over fitted and how would I know if I should mix some of my 15 independent variables instead of making 15 models with one variable each?

I know I can compare the forecast errors of each model and such but I feel like I have to experiment with the forecasting. Should I try to predict from n-2,n-1,n and aggregate? It feels like depending on the case I'm using to start forecasting, the answer might be good or bad.

[Anonymous No.7919693]

>>7919594
Consider the vector space R3.
[1,0,0] and [0,1,0] are in R3, but they do not span R3.

[Anonymous No.7919698]

>>7919619
Gauss elimination

[Anonymous No.7919705]

>>7919698
elaborate

[Anonymous No.7919733]

>>7919705
Let's take the span of u_1,..u_k and you ask whether v belong there. this is the same as deciding whether the equation
a_1*u_1 + ... + a_k*u_k = v
has a solution (note that the variables are the a's, not u's). as the u's are merely columns of numbers, this is actually a system of linear equations which can be solved (or proven that there's no solution to it) using the gauss elimination

[Greene No.7919744]

I just wrapped up multivariable calculus. It was fun. What math should I study next?

* I'm not in college, MOOC or self-taught resources preferred.
* My interests are Math & Physics.

[Anonymous No.7919758]

>>7919744
do you learn the theory as well (theorems and proofs, do you know anything about metric spaces, measure theory) or do you just do exercises ?

[Anonymous No.7919791]

can a vector be any rank n tensor?

[Anonymous No.7919797]

>>7919744
set theory->real analysis->complex analysis->functional analysis

[Anonymous No.7919826]

>>7919733
I'm fucking retarded, I just had to show that the matrix is inconsistent

[Anonymous No.7919842]

>>7919619
Let's say v1, v2 and v3 are three vectors (let's say in 3D space but you can take any dimension though you would need more/less vectors) that are linearly independent (none of these can be written as linear combination of two others).

Is v4 part of the subspace spanned by {v1, v2, v3}? What you're really asking is if there exist scalars a, b, c, such that a*v1 + b*v2 + c*v3 = v4. If you're the least bit familiar of solving these systems you'd see that you can turn this equation into matrix form and start reducing to echelon form, the process of which is called Gauss elimination.

Now if you want to know if {v1, v2, v3} span 3D you can either use the dummy but logical method by showing that a linear combination can be found for arbitrary v4. Easier though is using the invertible matrix theorem, which is a set of equivalent propositions. If you can reduce the matrix you constructed to echelon form and every column is a pivot column, then the matrix is invertible and hence the vectors 3D space.

[Anonymous No.7919870]

Is this an editorial mistake? None of these choices are correct.

[Anonymous No.7919929]

>>7918315
Anyone here good at real analysis?

I'm trying to use the ratio test on
[math] \sum_{n=1}^{\infty}\frac{(n-1)!-3n}{5\cdot2^n+2(n+1)!} [/math]
But I keep on getting that the limit of the ratio of any two consecutive terms is 0 (by dividing through by the (n+2)! term), although apparently the answer is that the test is inconclusive.

Where have I gone wrong?

[Anonymous No.7920041]

What does "coordinate vector relative to a given basis" mean?

[Anonymous No.7920066]

>>7920041
I would say it means the column of coordinates

[Anonymous No.7920086]

>>7920066
what the fuck does that mean?

[Anonymous No.7920097]

>>7920086
take a vector take a basis take its coordinates in said basis write them in a column done

[Anonymous No.7920101]

>>7920041
Write down each coordinate with respect to that basis in an nx1 matrix.

[Anonymous No.7920319]

If I'm trying to show that [math]|f(n)| = 0[/math] and I use something like [math]|f(n)| \leq g(n) < h(n) \leq j(n)[/math] and [math]\lim_{n=0}^{n \rightarrow \infty} j(n) = 0[/math], is that OK? I can't think of an obvious counterexample, but if it's wrong then I'm sure that there is one.

[Anonymous No.7920322]

>>7920319
I have no clue why I've written [math]\lim_{n \rightarrow \infty}[/math] like that.

[Anonymous No.7920330]

What's a PhD intern?

Context:
>We will be accepting PhD intern applications from next year.

Does it mean they accept interns who are pursuing their PhD at the same time?

[Anonymous No.7920336]

>>7918987
The n quantum number can never be zero.

[Anonymous No.7920467]

I'm a freshman physics major and my class is going through statistical mechanics right now. Did anyone else have trouble with this their first time through? Does it get easier? Any tips?

[Anonymous No.7920503]

>>7920319
If |f(n)| < j(n) (for large n) and j(n)->0, then f(n)->0. But if you actually need to show that f(n) IS 0 (for all n? for large n?) that's not enough.

[Anonymous No.7920504]

>>7920503
Sorry, I'm a bit tired and that question was worded terribly. Should've written [math]\lim_{n \rightarrow \infty} f(n) = 0 [/math] instead. But that'll do, thanks.

[Anonymous No.7920578]

If I have no outside of school interests in STEM (maybe besides a little programming and messing around with UNIX), what major would be the best to go into for purely the job prospects? engineering or something like CS/Stat or Finance?

[Anonymous No.7920590]

>>7919425
There are many situations in which you can prove something is a bijection without directly proving surjectivity. For instance, if you have a function from a finite set S to itself, then any injective function is bijective and therefore surjective (in fact, for these functions, being injective, surjective and bijective are equivalent). Linear Algebra also has several methods by which you can indirectly prove injectivity or surjectivity (or both) using higher-level properties of the function you're considering (study its rank, kernel, eigenvectors or whatever, all of that is pretty much the same idea).

In general though, or for your example in particular, I can't think of such a trick.

[Anonymous No.7920626]

>>7920467
stat mech is typically one of the worst-taught courses with the most variation in the presentation of its material. Feel free to check external sources, look at other authors and how they present the material. Find a way to have it make sense to you.

This is good advice for any subject giving you trouble.

[Anonymous No.7920878]

>>7919929
https://en.wikipedia.org/wiki/Convergence_tests

[Anonymous No.7921467]

>>7920330

Bump

[Anonymous No.7921470]

>>7920336
Why not? Is there a reason for it mathematically or something?

[Anonymous No.7921843]

X is the pinnacle of Y.

X is the definition of Y.

Can someone give me the different word, I can't remember it for the love of God. English is a second language and it's frustrating me to the ground.... What word am I thinking of?

[Anonymous No.7921850]

What branches of science should I read into if I want to understand the brain fully and the things that affect it? It may be more than one subject which if so is fine. For extra detail these are some of the things that interest me: NoFap, motivation, happiness, depression, discipline, food's affect on the brain, anger. All that shit. I'm sick of the pseudo-science and lies. I want to know the cold hard science of it all.

[H No.7921859]

>>7919598
No, not every embedding is proper.

[Anonymous No.7921868]

Ok - new dumb question:
If you want to score a likert scale (e.g. PANAS), do you use the median or the mean?
Since likert scale answers are always ordinal, I know it should be the Median - however many papers I've seen still use the Mean, as if it were a scale. What do you think?

[Anonymous No.7921979]

This is more of a syntax problem. I understand the concept of modulo but I'm confused by some aspects of the definition
If given, for example, a congruence relation 24|a-b, with the consequent classes:

Z/nZ = {[0], [1], .. , [23]}
with [0] = {..., -24, 0, 24, ...}, [1] = {..., -23, 1, 25, ...}, etc.

Why do you have expressions like

[a]n + [b]n = [a + b]n
[12]24 + [21]24 = [9]24

in the wiki page (but also from other sources) https://en.wikipedia.org/wiki/Modular_arithmetic#Integers_modulo_n ?

I understand 33 being part of the congruence class of 9, but how does that expression make sense if we're working with sets and not elements?

[Greene No.7922099]

>>7921843
X is a Function of Y
X is defined in terms of Y
X is dependent on y

One of these? Working in a second language is tough.

[Greene No.7922103]

>>7921868
>If you want to score a likert scale (e.g. PANAS), do you use the median or the mean?

Mean is used when the data fits a normal curve, and not skewed by outliers.

Median is used when the data would not be well represented by a normal curve, i.e. if the data is skewed to one side or another by outlying data points.

[Anonymous No.7922107]

>>7921850
Neurology?

[Anonymous No.7922127]

>>7921979
Well, the thing (and you seem to have understood it) is that 9 is in the congruence class of 33 and, therefore, the two sets [9]24 and [33]24 are *identical*. The notation is simply a shorthand for {...,-26,9,33,...}.

[Anonymous No.7922134]

>>7918318

>the assignment is due soon

He didn't really try to hide it, smart-guy.

[Anonymous No.7922137]

>>7919929

The limit is either one or D.N.E. if the ratio test fails.

[Anonymous No.7922138]

>>7922127
Exactly, but that's the thing: are those operations between two sets defined in algebra? How do you "sum" two congruence classes given that example?

[Anonymous No.7922143]

>>7922138
>How do you "sum" two congruence classes given that example?
It's defined to be the congruence class of the sum of representatives for the two congruence classes. So [12]24 + [21]24 = [33]24, which is exactly the same set as [9]24. We can define addition to be whatever we want, and this definition captures what we like about modular arithmetic. It makes more sense from the general viewpoint of quotient groups, I think.

[Anonymous No.7922153]

>>7921979
You can add sets

[eqn] A + B = \{ x + y | x \in A, y \in B \} [/eqn]

[Anonymous No.7922196]

How do I prove [math]\frac{y}{x}\ln(\frac{y}{x})[/math] is Lipschitz-continuous given that [math]\left | x - 1 \right | \leq \frac{1}{2}, \; \left | y - e \right | \leq \frac{e}{2}[/math]?

Ive tried expanding the logarithm functions by using the rule ln(x/y) = ln(x)-ln(y) and, using the fact that ln is strictly increasing, substituted in the values in which they take on their local maximum. Using this I can prove

[math]\left | f(x,y) - f(x, z) \right | \leq D + C \left | y - z \right |[/math]

for D := | 3e ln(3e/2) - e ln(e/2) |, C := 2 ln(3/2)

But the D-component is bothering me.

[Anonymous No.7922203]

>>7922196
[math] \frac{y}{x} \ln(\frac{y}{x}) [/math]

Correction

[Anonymous No.7922206]

>>7922143
So the expression deals with members while still implying their belonging to the class, kind of?

>>7922153
How does that give back a set?

[Anonymous No.7922238]

When should I put a modulus extracting a root square, when should I put +- after extracting it etc?

Can some anon explain this fucking thing to me please? Mock me all you want but please explain it.

Also I am not underage, just retarded.

[Anonymous No.7922241]

>>7922206
>So the expression deals with members while still implying their belonging to the class, kind of?
Yeah, I'd say so. Another vantage point is slightly more abstract, but perhaps more conceptually gratifying. Nobody thinks about these things in terms of the equivalence classes after learning that it works, anyways. I'd prefer to think that we're taking our set (the integers in this case) and sort of "gluing together" all of the members in the same class, getting a new set with finitely many points. We can think of a member of the new set equally well in terms of any of the points that were glued together to form it.

[Anonymous No.7922249]

>>7918315
What's a good book on mathematical proofs?
And what about number theory?

[Anonymous No.7922282]

>>7922099
Haha, nah man. I should have specified more instead of using X and Y on a Maths board.

Here's an example:
>OP is not a faggot.
>Lmao, are you serious? Dude, OP is literally the pinnacle/definition of a faggot.

Typing "definition synonym" on Gave me the definition of "synonym" rather than synonyms of "definition".

Anyway, I looked up synonyms of "incarnation" and got EPITOME... That's what I needed.... I was so frustrated.

[Anonymous No.7922667]

Can it be generalized that anything finite is infinitely small compared to something infinitely large?

[Anonymous No.7922676]

TL;DR version: At what level of involvement is it generally expected (or even mandated) for a person's name to end up on an academic paper?

Long version: I'm an undergrad research assistant in a lab and my prof has been helping a post-doc write a paper. The paper is extremely behind schedule, the Air Force expects it in a week and it's not even half done, because the post-doc has pissed away the past year without making any real headway on it, so it's been a big priority in the lab and I've been given a lot of work on it. The idea initially was for the post-doc to provide me with the content and I would write the actual paper, but this week the post-doc apparently collapsed "due to stress" and is now in the hospital and can't keep working on the paper. This has led to the prof and I splitting up the remaining research, with me doing as much of the grunt work that I can and the prof doing the heavy lifting on the bits that are just completely above my paygrade.

The question is, can I expect this paper to end up with my name on it, or as a URA should I just expect to not get any mention and to just deal with it? I don't really know how these things work, so at this point I'm curious to see if this'll end up being the start of my C.V.. If so, I might actually have to start giving a fuck about its quality...

[Anonymous No.7922696]

Since any point outside the boundary of a fractal set generated by iterating a complex function escapes to infinity under iteration by going through a certain trajectory of points, is there any fractal rendering software that can show me the trajectory in real-time when moving the cursor over the set?
Also, how to formally compare these trajectories?
Is the change of trajectory sometimes not smooth when comparing the trajectories of two or more neighbouring points?

[Anonymous No.7922749]

How come if I want to solve for m in this formula E=mgh I get E/gh=m. But when i try and solve for R in I=U/R the answer is supposed to become U/I=R but solving it in the way with E=mgh I get I/U=R? Same with when I want to solve for r in F=mv^2/r I get F/mv^2=r and again I got this by solving it the same way with E=mgh, though my textbook makes the claim that it should be mv^2/R=r. What is it that I am doing wrong? Why is it like that? I don't really get why the positions of the numerator and the denominator should be switched, can some please explain this to me?

[Anonymous No.7922763]

Why is it when I assign the drawn sign convention for the circled area, I get the wrong answer? Doesn't it not matter which convention you use?

For reference, the answer comes out to be 0.504sin(t+19.1).

[Anonymous No.7922805]

Take I = U/R. Multiply both sides by R to find IR = U, then divide by I to find R = U/I.

F = mv^2/r
Fr = mv^2
r = mv^2/F

[Anonymous No.7922816]

>>7922749
>>7922805

[Anonymous No.7922818]

>>7922805
>>7922816
Thank you, this clears a great deal up

[Anonymous No.7922820]

If donkeys and horses are not the same species, why can they produce an offspring at all? And in very rare cases, some mules are fertile. Hows does science explain that?

[Anonymous No.7922822]

>>7922818
*clears up a great deal

[Anonymous No.7922853]

If y=cot(x) in degrees is a hyperbola that can be moved closer or further to zero diagonally, vertically and horizontally, can be stretched, and can be changed with things I have to yet to know of, can you change the shape of a cotangent hyperbola so that it satisfies every point of an inverse cotangent hyperbola in the ++ quadrant? For instance, could I plug (2) into some sort of cotangent formula that would give me the angle of a right triangle with a slope of 1:2 in the same way that arccot does, instead of that shitty 28 number?

[Anonymous No.7922915]

>>7922676
Ask your professor. We can't answer this question.

[Anonymous No.7923056]

Hey /sci/, I have a week to learn derivatives before my exam. In a standard calc 1 course is this feasible if I do nothing but study this weekend?

[Anonymous No.7923101]

Is Kepler's law:
T^2/r^3 = (4π)^2/GM
OR
T^2/r^3 = 4(π)^2/GM

[Anonymous No.7923502]

>>7922915
Ok. I was only wondering if there was a standard practice with regards to that. If the professor has the final say, then the professor has the final say.

[Anonymous No.7923594]

is there an inverse to sigma,
like if two sums have the same domain with two different function in them, but they're equal to each other, are the functions equal as well

[math]
\sum _{k=1}^{n} \sum _{j=k}^{n-1} (d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}))) &= 0 \\
\sum _{k=1}^{n} \sum _{j=k}^{n-1} (d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}))) &= \sum _{k=1}^{n} \sum _{j=k}^{n-1} 0 \\
d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1})) &= 0 \\
1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}) &= 0 \\
1 &= cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1} \\
1 &= cos( \theta _{k} - \theta _{j+1}) \\
cos^{-1}(1) &= \theta _{k} - \theta _{j+1} \\
0 &= \theta _{k} - \theta _{j+1} \\
\theta _{k} &= \theta _{j+1}
[/math]

can i just go ahead and do that
also is

[math]
\theta _{j+1}
[/math]

the same as

[math]
\theta _{k+1}
[/math]

[Anonymous No.7923604]

>>7923594
well then that broke

[math]
\sum _{k=1}^{n} \sum _{j=k}^{n-1} (d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}))) &= 0
[/math]
[math]
\sum _{k=1}^{n} \sum _{j=k}^{n-1} (d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}))) &= \sum _{k=1}^{n} \sum _{j=k}^{n-1} 0
[/math]
[math]
d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1})) &= 0
[/math]
[math]
1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}) &= 0
[/math]
[math]
1 &= cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}
[/math]
[math]
1 &= cos( \theta _{k} - \theta _{j+1}) \\ cos^{-1}(1) &= \theta _{k} - \theta _{j+1}
[/math]
[math]
0 &= \theta _{k} - \theta _{j+1} \\ \theta _{k} &= \theta _{j+1}
[/math]

[Anonymous No.7923612]

>>7923604
ok since i can't figure this out i just took a picture

[Anonymous No.7923753]

Can someone explain what t is used for, and what M(PL) is? And how the fuck can there be a sin(E) when E is not ever mentioned as a variable? Sorry that I don't know LaTEX.

[Anonymous No.7923845]

what's the difference between rank and dimension?

[Anonymous No.7923851]

>>7923845
Dimension is obvious, rank is the dimension of the vector space. So rank will be less than dimension when columns/rows aren't linearly independent.

[Anonymous No.7923892]

>>7923851
I still don't see the difference; when you have 3 vectors-for example but 2 vectors are linearly dependent, wouldn't both the dimension AND rank be 2?

[Anonymous No.7923953]

>>7923845
These aren't defined on the same objects. The rank is a quantity associated to a family of vectors, whereas dimension is a quantity associated to a vector space.
The relation between the two notions is the fact that the rank of a family of vectors is the dimension of the vector space that they span.

[Anonymous No.7924138]

What kind of object do you get if the radius of a sphere is increased without bound, so that one of its boundary points stays at the origin?
Is it just plane-like?

[Anonymous No.7924304]

>>7923845
Dimension(of a vector space) is the size of a basis for your vector space. Rank (of a linear transformation) is the dimension of the image of the transformation.

[Anonymous No.7924389]

If 0 is neither a negative or a positive number then why is it a member of R+?

[Anonymous No.7924422]

>>7924138
THEN WHO WAS SPHERE?

[Anonymous No.7925056]

What is actually going on when we're solving a linear equation system? Like, what is going on?

[Anonymous No.7925064]

How do I calculate the upper triangle matrix?
>>7925056
You're finding numbers which fulfil each equation?

[Anonymous No.7925070]

>>7925056
How much do you know about linear algebra ?

[Anonymous No.7925218]

>>7925070
Tbh not much. Started ACTUALLY studying maths for the first time in my life like, two months ago. (didn't touch maths at all during hs, now taking a gap year to learn hs maths completely since I got interested in physics). I know the principle of solving, and out of the 3 ways I know (substitution, comparison and method of opposite coefficients), comparison and substitution make sense. The third one doesn't. Why does it work?

>also sorry if the names of solving principles don't make sense in English, I just directly translated them from my language

[Anonymous No.7925872]

>>7918315
C++ question.

For some reason my programs constructor only works with literal strings. As in, the parameter

Token(p, "String");

will work, but

string user= "string"

Token(p, user);

will not work.

I don't know why.

Paste bin of function: http://pastebin.com/mSMaAnJG

Paste bin of header file with constructor:
http://pastebin.com/GMrht1CT

[Anonymous No.7925896]

>>7925872

Hey Abe.

My guess is that the signature of the constructor to Token is something like (typeof(T), char*).

string != char*

Look up c_str for C++ strings.

[Anonymous No.7925902]

>>7925896
I actually figured it out, and I'm not happy. Every time I call the function it will only be a correct call the one time, the second time the information gets corrupted. Its weird, but I'm working around it.

[Anonymous No.7925905]

>>7925902
>>7925896
forgot to post the picture, just for reference sake;

[Anonymous No.7925916]

>>7925905

What are you trying to implement, if you don't mind me asking? If you're trying to write some kind of interpreter or translator, you should look into tree-based parsing using CFGs as opposed to trying to do things like parentheses or expression matching manually.

[Anonymous No.7925945]

>>7921470
It would mean the electrons don't have energy and have fallen to the nucleus.

[Anonymous No.7925993]

First spring at my house and I live near a lake. Why the FUCK is it so loud? Once it gets dark there is a constant, loud animal buzzing and it's annoying as hell.

What creatures are making this noise

[Anonymous No.7926218]

>>7925064
Use gaussian reduction on the matrix (reduce to row echelon form).

[Anonymous No.7926221]

>>7923101
the second one

[Anonymous No.7926508]

>2a(x-1) is not always equal to a(2x-2)
WHAT

[Anonymous No.7926515]

>>7926508
It's is in R but not always in other rings

[Anonymous No.7926517]

>>7926508
fixed it

http://www.wolframalpha.com/input/?i=are+2*a*(x-1)+and+a*(2x-2)+equal

fucking bullshit

[Anonymous No.7926520]

>>7926515
Why wouldn't it be?

[Anonymous No.7926795]

[math] 1=e^0=e^{i2\pi} [/math]
[math] 1^i=e^{i0}=e^{-2\pi} \Rightarrow 1=\frac{1}{e^{2\pi}}[/math]
There must be some sort of rules to complex exponentials that prevents these sorts of fallacies. What are these rules and why do I never see them mentioned ever?

[Anonymous No.7926821]

>>7926795
>There must be some sort of rules to complex exponentials that prevents these sorts of fallacies.
Yes, they're called understanding what you're doing rather than pushing symbols around.

[Anonymous No.7926834]

[math] e^{i0} = e^{-2\pi} [/math] Do you know how to multiply by 0 ?

[Anonymous No.7926836]

In a quadratic function of the form y = ax^2 + bx × c, where a =/= 0, x^2 and x are the inputs, not the constants a, b, and c. Correct?

[Anonymous No.7926840]

>>7926795
i times 0 clearly returns 0 but lets be completely retarded and ignore that so that we imply that 2pi = 0 and then act surprised like a fucking moron when assuming that 2pi = 0 causes an impossible equality.

Yup, keep it up. Electrical Engineering major is it?

[Anonymous No.7927054]

Where does the internet from your data plan come from?

[Anonymous No.7927361]

>>7918315
C++ question. I want to have global variables that can be accessed from any function or file. How can I do this?

I already tried pic related to no avail;

[Anonymous No.7927362]

>>7927361
>C++ question.
>>>/g/

[Anonymous No.7927418]

>>7926840
Nowhere did he imply that you smug piece of shit. The complex exponential function is not one-to-one, so [math]\mathrm {e}^{i0} = \mathrm {e}^{-2\pi}[/math] does not imply [math] 0 = 2\pi[/math]. Did you actually read his whole post?

[Anonymous No.7927426]

>>7927361
bool fuckthissolution(){return true;}

[Anonymous No.7927434]

are mitochondria in neurons different from the mitochondria in eg fibroblasts or liver cells? maybe not morphologically but biochemically?

[Anonymous No.7928267]

so I'm applying for jobs

ive written some scripts for 4chan. for example, i wrote a script that reorganizes a 4chan thread based on number of replies so the posts with the most replies are at the top.

would it be a bad idea to put this on my resume?

thanks in advance. really appreciate it.

[Anonymous No.7928269]

>>7928267
to be more specific, im applying for programming/software development jobs.

[Anonymous No.7928274]

>>7927434
No. Your mitochondrial DNA is the same everywhere. It might be epigenetically expressed differently in those cells, but I don't think there's much of a difference.

[Anonymous No.7928276]

>>7928267
Yes, it's a bad idea. Also, not a very interesting thing to put on a resume. You might want to find some better examples of experience than 4chan scripts.

[Anonymous No.7928281]

>>7928276
got it. thank you for the kind honesty.

[Anonymous No.7928365]

I have a big head

[Anonymous No.7928455]

I have a scientific paper, see. I need to find papers that cite that paper. Google Scholar isn't giving me any hits so I want to know if there's an equivalent service elsewhere.

[Anonymous No.7929086]

>>7928455
i have a 3d vector where X is right, Y is forward and Z is up

i want to apply the following transformations, in this order:
>rotate around y axis (roll)
>rotate around x axis (pitch)
>rotate around z axis (yaw)

is there a more elegant or more efficient way to get exactly this transformation result than to do three consecutive 2d rotations?

[Anonymous No.7929088]

i have a 3d vector where X is right, Y is forward and Z is up

i want to apply the following transformations, in this order:
>rotate around y axis (roll)
>rotate around x axis (pitch)
>rotate around z axis (yaw)

is there a more elegant or more efficient way to get exactly this transformation result than to do three consecutive 2d rotations?

[Anonymous No.7929097]

I wanna do both math and EE at uni, what do? I love math, but I don't want it to be my job.

[Anonymous No.7929257]

How else can I write [math]P(A,B|C,D,E)[/math]?

[Anonymous No.7929279]

What are eigenvalues/eigenvectors?

[Anonymous No.7929283]

>>7929257
Is it...
[math]P(A,B|C,D,E) = \frac{P(A,B,C,D,E)}{\sum_{A,B}P(C,D,E)}[/math]?

[Anonymous No.7929288]

>>7929283
Let's try again
[math]P(A,B|C,D,E) = \frac{P(A,B,C,D,E)}{\sum_{A,B}P(C,D,E)}[/math]

[Anonymous No.7929291]

>>7929288
Whatever, is this correct?

[Anonymous No.7929526]

Hey faggots

What is the difference between a quadratic equation and a quadratic function?

[Anonymous No.7929565]

>>7929526
equation: find values of x that make the equality true

function: put it any value of x and get its corresponding value f(x)

[Anonymous No.7929652]

>>7929526
One is an equation, another is a function.

[Anonymous No.7929696]

Im 1 class short of a math minor. Im a physics/ee dual major, with a focus on nonlinear optics, and I've taken ode and pde's. The suggested course is linear algebra, but its a dumbed down course, and I already know linear because its used as a tool in many of the physics classes.

If I plan to go to grad school, what would be a decent class to take?

[Anonymous No.7929753]

>>7929652

Functions are equations. They're equations that express one variable in terms of another.

[Anonymous No.7929766]

If the first law's differential form is du= dw+dq why is the integral DU= W+Q and not DU=DW+DQ?
How do I right down the process to turn one to the other in a way that justifies the symbols?

[Anonymous No.7929772]

>>7929753
No, a function [math]f [/math] is a tripel [math](A,B,\Gamma) [/math] with [math] \Gamma \subset A \times B[/math] such that for each [math] x \in A [/math] there is a exactly one [math]y \in B[/math] with [math](x,y) \in \Gamma [/math].

We just use the notation [math]f(x) = y [/math] if [math](x,y) \in \Gamma [/math].

[Anonymous No.7929777]

>>7929772

That is not the definition taught to high school kids. Fucking hell, some of you are utter autists.

[Anonymous No.7929827]

>>7929777
it literally is. maybe not with that exact notation

[Anonymous No.7930629]

If one particle escapes from the box in Schrodinger's cat experiment and ends up collapsing the wave function of the cat, does that mean the particle contains a cat's worth of information?

And if so, assuming any equipment physically possible as well as infinitely powerful quantum computers, can one measure the particle then generate an atom-by-atom image of the cat from it?

[Anonymous No.7930800]

I'm doing this for Chemistry 101 and I just feel like I'm doing it wrong. Is this correct?

[Anonymous No.7930802]

>>7930800
XDDDDDDDDDDDDDDDDDDDDDD

[Anonymous No.7930810]

>>7930802

Yes, I know this is 8th grade stuff.

[Anonymous No.7930889]

Can someone solve this?
>inb4 Underage
I'm in CC Math pls no bulli

[Anonymous No.7930996]

>>7930889
Do you know what polynomials look like when you factor them?

[Anonymous No.7931035]

>>7929279
geometrically an eigenvector of a linear operator is one that may be scaled but is not rotated under the action of that operator.

sorry if that's wrong or incoherent. i am drunk

[Anonymous No.7931045]

>>7931035
babees first diffrential equations

[Anonymous No.7931211]

I'm still having a shit of a tough time deciding this and don't want to make an actual thread.
Would you rather do a 10-week research internship at Cornell in accelerator physics or at Columbia + Fermilab in HEP?

[Anonymous No.7931212]

>>7930800
just make sure you have the same number of atoms on the left and the right side

[Anonymous No.7931216]

>>7928455
pls

[Anonymous No.7931279]

This is regarding powers of matrix, obviously. No proof is offered. Can someone help me shed some light on this? A proof would be nice.

[Anonymous No.7931283]

>>7931279
Actually, nevermind. I was able to prove it myself.

See ya in a few months, /sci/, when I need some help with real analysis.

[Anonymous No.7931306]

>>7918400
Draw a picture of a hand closed into a loose, but sensually held fist.

Draw an arrow after this picture. If you don't know how to do this just use your best guess.

Now draw a picture of the same hand holding up it's index finger, also known as the pointer finger. Next to that put a note that says one. For reference the number one looks like "1" without the quotations

Draw a plus sign after this picture. It should look something like "+" without the quotation marks.

Now draw a picture of the same hand that is only holding up a middle finger, make sure this one is larger than the other ones because it's important. Ideally it should take up an entire page on it's own. Shading is also important because the middle finger should be portrayed in stark relief to the background. Next to this make another note that says one.

Draw an equality sign after that. It will look something like "=" without the quotations.

Now, here comes the hard part. Draw the same hand except in this picture the hand should be holding up the both the index and the middle finger at the same time. Make sure that it's all to scale so there can be no confusion as to the proportions. Finally next to this you should make another note, this note should say two. Again, for refrence, the number two looks like "2" without quotations.

Now sign the paper with your blood and present it to your instructor. After you do this nod and stand there staring soullessly into their eyes until you are dismissed. It is very important that you say nothing, simply leave when you are told.

[Anonymous No.7931634]

Why is the first aspect ratio equivalent to x : x^2?

[Anonymous No.7931637]

>>7931634

Wait a minute, may have just answered my own question. Is it because 1 : x can be multiplied by x, giving x : x^2?

[Anonymous No.7931651]

>>7931637
yes

[Anonymous No.7932707]

What kinda minor are you supposed to have as an engineer? I'm a first year electrical engineering student and haven't even decided what I want to specialize in and they're already asking me about a minor. I wanna run a business in the future so should I do management or just go computer science/information tech/automation and aim for either industrial applications or the consumer electronics market?

[Anonymous No.7932729]

How do I know when to use method of rings instead of method of cylinders and viceversa?

[Anonymous No.7932802]

Is this literally all that "gravitational waves" means?

[math]g_{\mu \nu} = \eta_{\mu \nu} + h_{\mu \nu}[/math]

where

[math]\Box h_{\mu \nu} = 0[/math]

in free spacetime?

[Anonymous No.7932807]

>>7932729
visualize the shape you are trying to integrate, or try one and if it gets hairy try the other.

also get good at recognizing what the general forms of surfaces are so you can see an equation and say "oh that's a paraboloid I will use whatever the fuck"

[Anonymous No.7932836]

>>7932802
Pretty much.

[Anonymous No.7932871]

What is an electron?
Seriously, I have no idea if it's considered matter or energy or somewhere in between, it's never been explained that well to me.

[Anonymous No.7933124]

What in the fuck is the Zariski tangent space every single book gives the same nothingness of information about it

> So you should just accept this definition for now, and later convince yourself that it is reasonable

[Anonymous No.7933142]

>>7919315
Vectors aren't arrows pointing in space; arrows pointing in space can be seen as vectors though.

[Anonymous No.7933145]

>>7929827
>literally

[Anonymous No.7933148]

>>7933142
Mathematicians are like Frenchmen: whatever you say to them they translate into their own language and forthwith it is something entirely different.

[Anonymous No.7933220]

Is my clitoris of normal length?

~2mm

[Anonymous No.7933348]

Now, I'm only asking this because I'm not aware of further problems/developments that came to in the Navier-Stokes equation, but...

What's the use of the stream function? How was it actually applied to solve something that cannot be solved without it?

[Anonymous No.7933374]

>>7933220
i am doctor and i will tell to you if normal
but to be certain i must see it

[Anonymous No.7934286]

https://www.youtube.com/watch?v=q9IWoQ199_o&index=3&list=PLyQSN7X0ro203puVhQsmCj9qhlFQ-As8e

What is the book that is used alongside these lectures?

[Anonymous No.7934296]

>>7923594
>>7923604
>leltex

Anyway, I found your problem. Use normal = instead of &=.

[eqn]\sum _{k=1}^{n} \sum _{j=k}^{n-1} (d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}))) = 0 \\ \sum _{k=1}^{n} \sum _{j=k}^{n-1} (d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}))) = \sum _{k=1}^{n} \sum _{j=k}^{n-1} 0 \\ d _{k} d _{j+1}(1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1})) = 0 \\ 1-(cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1}) = 0 \\ 1 = cos \theta _{k} cos \theta _{j+1} + sin \theta _{k} sin \theta _{j+1} \\ 1 = cos( \theta _{k} - \theta _{j+1}) \\ cos^{-1}(1) = \theta _{k} - \theta _{j+1} \\ 0 = \theta _{k} - \theta _{j+1} \\ \theta _{k} = \theta _{j+1}[/eqn]

Sorry about your question though, hope someone else answers it since I don't have the brain juice for that right now.

[Anonymous No.7934344]

>>7919315
You need to change your idea of a vector. A vector is basically an array of numbers that you can add. As soon as you can see something as such an array of numbers, then it is probably a vector of sorts.
For example, a polynomial [math]P = a_nX^n + \dots + a_0[/math] is characterized by its coefficients [math](a_0, \dots, a_n)[/math] and the addition is defined coefficientwise, "therefore" (there would ideally be some more things to verify but you catch my drift) it is a vector.
It's the same idea for matrices.

[Anonymous No.7934460]

How would I make a switch that is controlled electronically, and has a ten second delay?

I have a circuit that will output either 3.3V or 0V. I would like to make a circuit that detects 3.3V, waits ten seconds, then closes a switch. The switch should remain closed even is the 3.3V drops back to 0V, possibly requiring manual reset.

Is this easily achievable?

[Anonymous No.7934607]

>>7918315
how many stereocenters does d-glucose have, according to my teacher, 5, according to other sources, 4, wtf?

[Anonymous No.7935248]

How do I git gud at math? I feel like a retard getting stuck on a chapter for 1-2 days

[Anonymous No.7935260]

[math]\mathbb{Z}_9 ^\ast \cong \mathbb{Z}_6 [/math] , right? Latex pls be easy on me

[Anonymous No.7935364]

>>7934607
In chain form, it has 4, as clearly shown in Fischer projection.

In cyclic form, a fifth stereocentre is formed.
https://en.wikipedia.org/wiki/Anomer

[Anonymous No.7935686]

What kind of mental defect causes people to enjoy Depeche Mode?

[Anonymous No.7935688]

>>7935686
excuse me?

you obviously don't have a personal jesus

[Anonymous No.7935712]

>>7935364
fuck, the anomer, thanks anon

[Anonymous No.7935833]

What the fuck is an eigenvalue's algebraic/geometric multiplicity? I've been searching for hours bt couldn't find a good definition

[Anonymous No.7935840]

>>7935833
Let A be a nxn matrix and lambda be an Eigenvalue of A.
The geometric multiplicity of lambda is [math] \mathrm{dim}(\mathrm{ker}(A - \lambda I)) [/math].
The algebraic multiplicity of lambda is [math] \mathrm{dim}(\mathrm{ker}((A - \lambda I)^n)) [/math].

[Anonymous No.7935844]

>>7935840
what's the purpose of this?

I'm also confused with nullspaces/nullity

[Anonymous No.7935877]

>>7935844
Let's say you have a vector space V and a linear Operator T: V->V with Eigenvalues [math] \lambda_1 , \ldots, \lambda_k [/math] then you can use Eigenvalue theory to decompose the space and operator.
[math] V = V_1 \oplus V_2 \oplus \ldots \oplus V_k [/math]
[math] T = T_1 + T_2 + \ldots + T_k [/math]
So that when [math] x = x_1 + x_2 + \ldots + x_k [/math] with [math]x_i \in V_i [/math] we have
[math] Tx = T_1 x_1 + T_2 x_2 + \ldots + T_k x_k [/math]
If the matrix is diagonalisable those T_i will just be a multiplication with lambda_i and you can define a functional calculus:
[math] f(T)x = f(\lambda_1) x_1 + f(\lambda_2) x_2 + \ldots + f(\lambda_k) x_k [/math]

This allows to solve systems of differential equations exactly like a single differential equation.

For example the system [math] \dot x(t) = A x(t)[/math] with [math] x(0) = x_0 [/math] has the solution
[math] x(t) = \exp(t A) x_0 [/math]
and the system [math] \ddot x(t) + A^2 x(t) = 0[/math] with [math] x(0) = x_0 [/math] and [math] x'(0) = 0 [/math] has the solution
[math] x(t) = \cos(t A) x_0 [/math]

[Anonymous No.7935878]

>>7935844
Let V,W be spaces and t a transformation from V to W.

If I remember correctly, the null space was a subspace of W from where if you were to input that W vector into the inverse of t, you could get the zero vector of V.

Nullity is the dimension of this space.

Also nullity = dimension - rangespace

[Anonymous No.7935882]

>>7934460
It's not trivial, but definantly doable. You are going to want some kind of oscilator (probably a clock crystal) and a divider circuit followed by a latch of some description.

[Anonymous No.7935905]

Why have human beings yet to tackle the biggest issues, such as teleportation, time travel, planetary weather control. Are scientists being too lazy? Are we still waiting for a scientific einstein-esque messaih? Are these technologies simply to big of a jump, such as it's going to take centuries of small advancements rather than one big "aha?

[Anonymous No.7935912]

>>7935905
I bet you watch a lot of Michio Kakuld shows Discovery(kids) channel

[Anonymous No.7935916]

>>7935912
i don't watch tv or download actual shit

[Anonymous No.7935934]

>>7935905
they're impossible or massively impractical

[Anonymous No.7935938]

>>7935905
we already have weather control to some degree

see HAARP

[Anonymous No.7935949]

at 3 mins

https://www.youtube.com/watch?v=RX3IOHpe6sY

[Anonymous No.7935952]

I'm supposed to do an analysis of stainless steel to determine what type of stainless steel it is.
So far I've come up with XRF, AAS and a thermometric titration. I've been thinking about regular spectroscopy, but I'm doubtful it will give reliable results.
Anyone got any suggestions?

[Anonymous No.7935955]

>>7935934
so they've been investigated so thoroughly that they're proven to be impossible?

[Anonymous No.7935970]

>>7935878
Nullspace is everything in V which maps to 0.

[Anonymous No.7936013]

Pic related, i am really confused at the moment, how do i get from one step to the other?
It's about finding the total impedance and that wouldn't be much of a problem but i have to write it down without calculating it. I don't get how i can simplify it like in the picture, and how to get everything into one fraction only.
Any help is greatly appreciated.

[Anonymous No.7936500]

I have a question regarding foreigners enrolling in American institutions for graduate studies.

Can anyone please walk me through the admission proccess to a good University in the USA — I'd really like if you took an Ivy League school as an example even though I realize how difficult they are to get admitted to — in the areas of Physics/Astronomy?

1. How does financial aid work in general (I'm aware it may change from institution to institution)? Does it cover all costs with utility/food/housing/miscellaneous expenditures? Do you have to work for the University to be entitled to that?

2. How do scholarships work? Are full tuiton ones hard to get? Can you combo a full tuiton scholarship with the financial aid above if they're both provided by the institution? What if they're provided by different organizations?

3. Can you recommend some scholarship programs in the USA?

3. What weighs more the GRE scores or your undergraduate record?

4. How important are the recommendation letters compared to the GRE scores and undergratuate record?

5. How important is the "who" writes the letters of recommendation?

6. How important is it that the author of said letters was a former alumnus of the institution they're being sent to?

7. How does the US higher education academic calendar works? Are academic periods divided into semesters or what?

8. When do admissions normally begin each year for graduate programs?

Thank you in advance.

[Anonymous No.7936514]

>>7936500
First, learn what the American flag looks like, faggot.

[Anonymous No.7936740]

>>7936500
The Ivy League is an athletic conference. I wouldn't use that as a criterion for a good physics grad program.

[Anonymous No.7936743]

>>7936013
It's all common denominator stuff. 1st step gets rid of the fraction in the denominator. 2nd step adds the jwl to the fraction. Then you combine everything.

I'm an EE. This was a fun part of circuits.

[Anonymous No.7936751]

>>7936743
I figured that I would be more explicit. All I did was multiply by one twice and add.

[Anonymous No.7936760]

>>7936743
>>7936751
Alright thanks a lot, i ended up using the wolfram alpha app on the phone to get a step by step solution and it was quite helpful actually.
Even so the way you are doing it is way easier to understand.

[Anonymous No.7936969]

>>7935905
First off, this truly is a stupid question

[Anonymous No.7936976]

>>7935260
Figured it out, it is (^:
Quite interesting desu

[Anonymous No.7937015]

My teapot has an iron exterior and a glazed interior.

It seems like if there is boiling water inside any moisture on the outside evaporates. So I put boiling water inside whenever I end up getting some drops on the outside by mistake.

Does this reduce chance of rusting?

[Anonymous No.7937484]

>>7932871
bump

[Anonymous No.7937493]

This is pretty stupid, but let's see if I'm not alone here

Which one is it?

[Anonymous No.7937532]

So in class I was told light emitted by a body of a given temperature cannot heat something higher than that temperature.
Why is this?
I tried getting an explanation from one of the tutors, but we didn't get anywhere because it didn't make sense they were saying that in the case of an object as hot as the sun having a huge amount of sunlight lensed onto it there would be more photons going from the object to the sun than the sun to the object.

[Anonymous No.7937616]

Also, another thing that confuses me about that stuff with the question above is that it implies an infrared laser cannot cut metal because metal glows in the visible spectrum before it melts.

[Anonymous No.7937759]

>>7937532
>>7937616
makes no sense to me

[Anonymous No.7937785]

>>7937759
Could you please not do that?
If someone is skimming through the thread looking for questions to answer, they'll focus on ones without replies.
It's kind of a form of unintentional trolling to reply without give an answer or a useful answer.

[Anonymous No.7937793]

>>7937493
that is a really shitty question with shitty answers because both the 2nd and 3rd can be correct given circumstance and the type of gene/disease process. Since Gene A not being expressed could be the link with disease B or the mutation from gene A could result in disease B like a number of cancers.

[Anonymous No.7937801]

Just got to writing names from formulas in Organic. Why do a lot of common substances with rings not use the "cyclo" nomenclature?

Can someone explain to me why, for example this molecule
(3,4--methylenedioxymethamphetamine) is not named
3,4-methylenedioxy-cyclopentene-3-prop-2-dimethylamine?

What am I doing wrong?

[Anonymous No.7937812]

>>7937801
lolno

Its IUPAC name is (R) 1-(benzo[1,3]dioxol-5-yl)propan-2-amine.

[Anonymous No.7937814]

>>7937785
it's a kind of an answer, how should i elaborate, if you send energy in the form of light to a body and the body absorbs it, its temperature increases

[Anonymous No.7937819]

>>7937801
>>7937812
Whoops wrong molecule. Left out the N-methyl bit my mistake.

(RS)-1-(benzo[d] [1,3]dioxol-5-yl)-N-methylpropan-2-amine.

[Anonymous No.7937822]

>>7937801
Probably because the latter is long as fuck compared to the methamphetamine one

[Anonymous No.7937823]

>>7937819
So when you're naming a group on a chain coming off of a ring like that, you start over counting the carbons in the chain at the end of the ring??

[Anonymous No.7937829]

>>7937822
but longer chemical names are cooler, anon.

[Anonymous No.7937854]

>>7935905
>Why have human beings yet to tackle the biggest issues, such as teleportation, time travel, planetary weather control. Are scientists being too lazy?
scientist cannot even prove that you were born, that you will die and that you exist as a human being

[Anonymous No.7938290]

Thinking on going for a Physics minor. Currently doing a CE major, is it worth it ?

[Anonymous No.7938329]

can someone please list me good books or important topics in math regarding computer science?

[Anonymous No.7938343]

>>7938329
http://www.goodreads.com/book/show/14411310

[Anonymous No.7938357]

Is the sky blue because it's the color of the ocean of gas mixture we stand at the bottom of?

[Anonymous No.7938578]

>>7938357
it's mainly because of rayleigh scattering

http://spaceplace.nasa.gov/blue-sky/en/
http://physics.stackexchange.com/questions/28895/why-is-the-sky-not-purple

[New TeX User No.7938600]

Hi, I'm teaching myself calculus with "Calculus: An Intuitive and Physical Approach", by Morris Kline.

Not that it's pertinent to this post, but, I've been studying computer science / programming for two years and have started to take an interest in math, to the point that I'm beginning to wonder if pursuing a math degree would be a better choice. Anyways...

I'm on chapter three and have been stuck on this problem for a while (mostly because I realized I had been multiplying fractions incorrectly *queue laughter*). Normally the answer is given, however the book doesn't give the answer for this problem so I can't check my work.

I'd just like some validation - is my solution correct? I feel like I may be wrong because I couldn't find 7 in my book's appendix's trigonometry table.

Third time's the charm guys, I found the TeX for newline so I didn't have to use a bunch of math tags... Sorry...

[math]m_2=-\frac{4}{3}, m_1=\frac{4}{4}\\
\tan\theta=\frac{m_2-m_1}{1+m_2m_1}\\
\tan\theta=\tan7\\
\theta=8.144\deg[/math]

[New TeX User No.7938612]

Hi, I'm teaching myself calculus with "Calculus: An Intuitive and Physical Approach", by Morris Kline.

Not that it's pertinent to this post, but, I've been studying computer science / programming for two years and have started to take an interest in math, to the point that I'm beginning to wonder if pursuing a math degree would be a better choice. Anyways...

I'm on chapter three and have been stuck on this problem for a while (mostly because I realized I had been multiplying fractions incorrectly *queue laughter*). Normally the answer is given, however the book doesn't give the answer for this problem so I can't check my work.

I'd just like some validation - is my solution correct? I feel like I may be wrong because I couldn't find 7 in my book's appendix's trigonometry table.

The mysteries of /sci/ TeX usage escape me...
Hi, I'm teaching myself calculus with "Calculus: An Intuitive and Physical Approach", by Morris Kline.

Not that it's pertinent to this post, but, I've been studying computer science / programming for two years and have started to take an interest in math, to the point that I'm beginning to wonder if pursuing a math degree would be a better choice. Anyways...

I'm on chapter three and have been stuck on this problem for a while (mostly because I realized I had been multiplying fractions incorrectly *queue laughter*). Normally the answer is given, however the book doesn't give the answer for this problem so I can't check my work.

I'd just like some validation - is my solution correct? I feel like I may be wrong because I couldn't find 7 in my book's appendix's trigonometry table.

The mysteries of /sci/ TeX usage
[eqn]m_2=-\frac{4}{3}, m_1=\frac{4}{4}\\
\tan\theta=\frac{m_2-m_1}{1+m_2m_1}\\
\tan\theta=\tan7\\
\theta=8.144\deg[/eqn]
[eqn]m_2=-\frac{4}{3}, m_1=\frac{4}{4}\\
\tan\theta=\frac{m_2-m_1}{1+m_2m_1}\\
\tan\theta=\tan7\\
\theta=8.144\deg[/eqn]

[Anonymous No.7938636]

>>7938612
>You cannot delete posts this often.
I'm sorry guys, this is my first time using TeX and I keep screwing up.
[eqn]m_2=-\frac{4}{3}, m_1=\frac{4}{4}\\
\tan\theta=\frac{m_2-m_1}{1+m_2m_1}\\
\tan\theta=\tan7\\
\theta=8.144\deg[/eqn]

[Anonymous No.7938670]

>>7938600
>>7938612
>>7938636
Reminds me when I was new to /sci/'s LaTeX. Don't worry about it too much, it's just >leltex acting up.

Add a few more spaces such that it doesn't screw up the equation and it SHOULD be fine. At least, the chances of the equation coming out as it should increases quite a lot.

[eqn]m_2 = - \frac{4}{3}, m_1 = \frac{4}{4} \\
\tan{\theta} = \frac{m_2 - m_1}{1 + m_2m_1} \\
\tan{\theta} = \tan{7} \\
\theta = 8.144 \deg[/eqn]

[Anonymous No.7938698]

>>7938670
Thank you very much.
Since that post I did some research and installed a bunch of TeX command line programs on my server, as well as ImageMagick (already have ImageMagick on my desktop).
I'm working on converting a .tex file into a .png, but am stuck on errors so far.
I'm happy, today I can say I didn't waste my time. I learned some new math, how to use basic Latex and even learned how to apply it with some command-line programs!

[Anonymous No.7938720]

>>7938670 here, continuing.

>tan 7
Actually, if the rest of the equation is correct, then tan θ = 7, so θ should be [math]\tan^{-1}{7}[/math] instead.

>>7938698
TeX here is a bitch to use so I try to avoid it where possible, but sometimes it's just unavoidable.

[Anonymous No.7938790]

Any tips for interviews? Might have to fly out for a big one in a few weeks. Any tips? The position in for engineering, but it's more in a lab environment with plasma phys experiments.

[Anonymous No.7938920]

How would one cluster tweets into praise, complaint, neutral?

For example suppose a sentence said
>I really like this!!
This would be a praise
>I really like the old one more!!
This would be a complaint
>this is okay
This would be a neutral

My current approach is to look into the dataset and choose one tweet that is clearly a praise, one that is clearly a complaint, and one that is clearly a neutral statement. Then go through each tweet, and compare it with my selected praise, complaint, and neutral, and group it with the one that's most similar. The biggest problem with this is that some tweets are very similar but are actually different. Like "I really like this" vs. "I really like the old one more!!".

Thanks in advance.

[Anonymous No.7939030]

I was reading my textbook's proof for the limit comparison theorem for series (pic related) and was wondering why the textbook made it so that epsilon is between 0 and L. Picking an epsilon greater than L will make (L-epsilon) negative but is that really a problem?

[Anonymous No.7939040]

Well, this only took all day.

[Anonymous No.7939152]

>>7939030
If [math]L - \epsilon \geq 0 [/math] then

[eqn] 0 \leq \sum_{k=1}^N (L - \epsilon) b_k < \sum_{k=1}^N a_k [/eqn]
So by the squeeze theorem convergence of [math] \sum a_k [/math] implies convergence of [math] \sum (L - \epsilon) b_k [/math].

This argument does not work if [math]L - \epsilon < 0 [/math].

[Anonymous No.7939214]

Hey guys, need help with converting this infinite if else chain into a for loop, any pointers? Python.

[Anonymous No.7939237]

How do you proof that all isometric transformation are biyective? I have the inyectivity but I don't know how to prove the supra.