/sqt/: Stupid Questions Thread

Yeah, I know but I don't know what method I should use for these problems. For example, here's a harder one:
[math](x-8)/(\sqrt[3]{x^2} + 2\sqrt[3]{x}+ 4)[/math]
Can you show me how you would solve this?

I'm nearsighted and I need glasses to use the computer. Now I'm doing it without glasses. I bring the monitor forward, close enough where I can just barely make out the letters without squinting or straining my eyes, and I fell like, if I will do this for long enough, that my sight will improve. Am I wasting my time with this?
pic related, me atm

Good job, you are retarded, son.

You got a better plan?
I've been wearing glasses non stop for the past 8 years and I have to change lenses almost every 2 years because my sight is getting progressively shittier, and just now I'm starting to think that it might be the glasses fault.
There's an entire industry behind this shit, why wouldn't they want to make me lose my vision, just so I have to buy new glasses all the time.

Can someone explain what the hell is "residual porosity" ?

I can't find any explanations for it, I'd really appreciate the help.

What's a good Master's Degree to get once I get my BSc in Math?

Sorry, I can't help you. You are past the point of redemption.

can someone either explain basic NMR to me, or link me something that can help. My O chem final is later today, I that's the only concept I can't wrap my head around

intensity - number of equivalent protons
multiplicity - number of equivalent neighbour protons, where singlet=0, doublet=1, triplet=2 and so on

the more electronegative a proton's surrounding is, the more it gets shifted to the left
tables of chemical shifts can be easily found in google

does there exist a polynomial bijection from QxQ to Q?

Fucking hell. That one was really tricky because I didn't know binomials very well.

All you have to do is know all the binomial formulas and look at what you are given. In this case you have the third root, so you need a binomial of grade 3 most likely.

Look up a^3 - b^3. The equation you have is given in the form (a^3 - b^3)/(a^2 +ba +b^2).
Solution is third root of x minus 2.

>Am I wasting my time with this?
Yes. The eye is not a muscle. While your sight can be corrected, it's not like this.

Okay, I managed to solve a few problems and I think I get it now. Thank you.

Prolonged zero gravity can really fuck up your body. Decreased bone density and muscle mass, accelerated Alzheimer's, decreased RBC and immune system, blood pressure and fluid redistribution.

Are there any positive health effects? Specifically for women, would a month or more in space be enough to have a permanent and positive effect on sagging boobs? Since it's caused by gravity, zero G would give the body could give the body time to heal and repair drooping boobs. Also, fluids tend to get redistributed in zero g, so should boobs get bigger too?

>The eye is not a muscle.
The eye does have muscles in it that help you focus and there are ways to strengthen them. Stenopeic glasses are lenses totally opaque with tiny holes in them. It's been proven to improve eye sight while wearing them and over time, improve eye sight while not wearing them. It's thought to be from training those muscles, but nobody is really sure how the glasses work.

Where does the +1 come from? Please help, I have final tomorrow

if R and S are posets of X is R intersect S a poset?

-(-9/4)^0 = -1

if you start using glasses your eyesight will get worse much faster

if you don't want glasses you're probs not wasting ur time

This is an really specific question but how can I practice translating concepts/sentences into algebraic equations?
I mean translating as in making equations off this sentence to solve the riddle.
"A princess is as old as the prince will be when the princess is twice as old as the prince was when the princess' age was half the sum of their current ages."

thats one of the most poorly constructed sentences ive ever seen

Let n > k > 2 be natural numbers. I have a set of n elements from which I wish to generate k-sized subsets such that no two subsets share 2 or more elements.
What is the maximum number of subsets I can generate this way?

Why can't I remember things?

I feel like I have a concept down decently while doing practice problems with steps I can look to for guidance, and even doing problems after that with no guidance I feel like I at least know what to do.

But one or two weeks later and I don't remember it at all and fail tests.

I somehow slipped through the cracks when transferring my math classes from my college and I'm taking ODE with no knowledge of series from calculus. Am I fucked?

Stupid bump

you didnt even ask a question, you just listed a set

redpill me on being a chemical engineer.

I'm not really following this, does anyone care to explain it to me in simpler terms (if possible).

Damn I feel like a brainlet

Remember when you did whole number division in elementary school, and your teacher would give you 27/5 and your answer would be 5 remainder 2?

This is exactly what they're doing. You find the biggest multiple of 5 that divides 27 and then subtract to find the remainder that's left.

There's a bit of work involved in proving that 0

So, in a=qb+r...
>a = the number you're dividing
>q = one number
>b = highest multiple of that number that divides into the original number
>r = remainder

correct? I still don't really understand the set that they made and the point of doing so.

tough question desu

mathoverflow.net/questions/21003/polynomial-bijection-from-mathbb-q-times-mathbb-q-to-mathbb-q

When finding the scalar potential of a vector field, how does integrating the components work?

Let me rephrase that. So to find the scalar potential, we would say that the vector field F = Mi + Nj + Pk, and (grad f) = \partial M /\partial X, \partial N / \partial y, etc...

To find f, we would integrate \partialM/\partial X with respect to X.... Can we do that? Like, can we integrate a partial derivative with respect to X? Sorry if my question doesn't make much sense, I don't really know that much about multivar

> "A princess is as old as the prince will be when the princess is twice as old as the prince was when the princess' age was half the sum of their current ages."
Work backwards, and remember that the difference between their ages never changes.

Current ages are x (princess) and y (prince).
When the princess' age is A, the prince's age is A+(y-x)

Half the sum of their current ages = (x+y)/2
Prince's age when the princess' age was that = (x+y)/2+(y-x)
Twice that age = (x+y)+2*(y-x) = 3*y-x
Prince's age when the princess' age will be that = (3*y-x)+(y-x) = 4*y-2*x
Which is the princess' current age: x = 4*y-2*x => 3*x=4*y => y=(3/4)*x.

The only option on the list which satisfies that is the princess is 40, the prince is 30.

First, if n < 2k, then it's zero.

Otherwise, there are C(n,k) = n!/(k!(n-k)!) ways to choose one subset, and C(n-k,k) ways to choose a second, resulting in C(n,k)*C(n-k,k) ways to choose an ordered pair of subsets. If you don't care about ordering, then halve that.

For m subsets, then it's C(n,k)*C(n-k,k)*C(n-2k,k)*...*C(n-(m-1)k,k) ways to choose an ordered m-tuple; divide by m! if you don't care about ordering.

[math]\int \limits _{C}\mathbf {F} (\mathbf {r} )\cdot \,d\mathbf {r} =\int _{a}^{b}\mathbf {F} (\mathbf {r} (t))\cdot \mathbf {r} '(t)\,dt[/math]
IOW, you first need to parameterise the curve (express it as a function from R->R^n). Then you can integrate the dot product of the vector field and the curve's tangent w.r.t. the parameter.

Note that a vector field only /has/ a scalar potential if the integral depends only upon the endpoints, regardless of the rest of the curve. In turn, this implies that the vector field is the gradient of a scalar field, which means that its curl is zero everywhere.

Yeah, actually exactly as you described it.

That's not his fucking question, but true.
He's saying, I have this vector field
[math]
\mathbf{F}
[/math]
with 0 curl, and knowing this, I want to find a scalar potential. To find this scalar potential, we effectively just have to do a "partial integral" with respect to each variable.

Conversely, if the field does have scalar potential, then it doesn't matter which curve you use, so you can just use a line segment, r(t) = p0*(1-t)+p1*t = p0+t*(p1-p0) => r'(t)=p1-p0.

So you can just take the component of the field in the direction of the line and integrate that.

Or you could use a piecewise curve where each piece is axis-aligned.

kind of. you want to find f so that f_x=M, f_y=N, f_y=P. So the first step would integrating M with respect to x. But you have to be careful with the constant of integration.

when you do a single variable integral, you need to add a +C because dC/dx=0 so the derivative can't "see" the extra constant.

In this case, when you integrate with respect to x, the "constant of integration" is really an arbitrary function g(y,z) of y and z, since the x-derivative of this is zero.

So f=integral(Mdx)+g(y,z), but you have no idea what g is. To solve for g, take the y-derivative of both sides and set it equal to N. Now try to take it from here.

i'm starting calc 1 next semester and i'd like a leg up
for someone who just finished pre-calc what should i study to get ready?

Professor Leonard on youtube.
I can guarantee you will get no less than a b if you watch his calc 1 series.

thanks!

I think you misunderstood the question. I'm not talking about how many ways there are to generate the subsets, I'm asking how many can you possibly generate given the rule.

Anyone able to help me figure out how to get to the answer?
The correct answer is A.

My method:
dI = dm*x^2
dm = 2M/D * dx (2 dots fit in each triangle)

dI = 2M/D * x^2 dx

I = 2M/D * Integral: x^2 dx
I = 2M/D * Integral: (D/sqrt(2))^2 dx
I = 2M/D * 1/6 * D^3
I = M/3 * D^2

Any help?

M/3*D^2 is closest to A among the available options, so it looks like you've already solved it.

Is that actually what they mean? That seems absurd. Would they not put the exact answer up there?

2R^2 = D^2
2mR^2 = mD^2

A. It's just 2*m*r^2 = m*D^2 (as r=D/sqrt(2)).

Why are you integrating? it's just two point masses (the ones on the axis of rotation are irrelevant).

I want to know how to find this stuff out through integration, likely the actual test will be harder.

I genuinely do not understand basic combinatorics.

If there are 3 boys and 5 girls seated randomly in a row, can someone point me in the direction of how to find the probability that the boys are side by side and the girls are side by side?

Why is x = 1/5, y = -1/5, and z = 2/5
Is it because x appears 5 times in total?

I'm not sure what you're asking, the results are pretty straightforward if you just solve the system through elimination.

There are two ways for this to occur: all the boys on the left or all the boys on the right. Next, there are 7 choose 3 possible arrangements of the the line (out of the 7 seats, you choose 3 to put boys in). Thus, the probability is 2/(7 choose 3) = 2/(7!/[(7-3)!3!]) = 2/35.

Well, thanks for trying but the solution key has the answer as [(2!)(5!)(3!)]/(8!), which reduces down to 1/28. It doesn't say how to get to that fraction of factorials though.

For some reason I decided 3+5 = 7. If you replace 7 with 8 in my explanation you get the right answer.

Oh duh, thanks man!!!

Did you mean boys are side by side AND girls, or either of the two?

I have a digital systems exam soon, any tips? I hope I can remeber how to do counters and basic shit. Also the fucking delay stuff is weird.

A motor boat needs a hours to go from A to B
down the river and n
eeds b hours to go from B to A (up the river) .
How many hours would it need to go from A to B if there were no
current
in the river?

Is bioinformatics a good field to get into if I want to solve interesting problems using programming?

Help, please. My answer is (v1+v2)/2, but I feel like its not correct

Seems right to me

It's (2*v1*v2)/(v1+v2)

what

Integration is only relevant when the mass is distributed over a volume with finite density.

For a point mass, it's just m*r^2.

For a volume, it's the sum of infinitely many infinitesimal point masses, i.e. an integral (in the most general case, a triple integral).

You cover the first half of the distance m in t1 = (m/2)/v1, the second half in t2 = (m/2)/v2.

with t = t1 + t2, the mean velocity v is a weighted mean like so:

v = v1 * t1 / t + v2 * t2 / t

Which is (2 * v1 * v2) / (v1 + v2)

If the distance between the two points is D, the first half of the trip takes time D/v1, the second half takes time D/v2, the total time is D/v1+D/v2 = D*(v1+v2)/(v1*v2), the total distance travelled is 2*D, so the average speed is 2*D/(D*(v1+v2)/(v1*v2)) = 2*(v1*v2)/(v1+v2).

Doing basic theory, and just to make sure, the notation a' means the inverse of a, right?

>theory

group theory :-)

Hey user, /lgbt/ here!
In the spirit of being politically correct, please use Xes and Xers in place of boys and girls next time. Thank you!
:^)

No, that's only true for abelian groups
In general, (ab)' = b'a'

To add: They might be using the ' notation to denote some homomorphism

I see, thank you

thats obviously a prime meaning the derivative of a :)

Aite, thanks. Does it have a name for non-Abelian groups?

You mean the ' operation?

Like I said here it's possible that they're using it to refer to some group homomorphism (a map which preserves the structure of the group) F: G -> G', with g' written in place of F(g), so that
F(ab) = F(a)F(b) becomes (ab)' = a'b'

>homomorphism

haha homo :-DDD ebin u algebraists are so fucking gay lmao@u

But alright, thanks man, appreciate the help :-)

Which of these options is better for career prospects:

1) get a PhD from a top university but don't publish anything particularly interesting before graduating

2) get a PhD from a low-to-mid-tier university but score a few high-impact publications during your PhD

?

[math]\color{#781b86}{\text{Do}}\color{#511da7}{\text{n'}}\color{#4136c0}{\text{t }}\color{#3e56cd}{\text{mi}}\color{#4274cd}{\text{nd}}\color{#4b8dc1}{\text{ m}}\color{#57a0ad}{\text{e }}\color{#66ae94}{\text{ju}}\color{#78b67c}{\text{st}}\color{#8ebb66}{\text{ t}}\color{#a5bd55}{\text{es}}\color{#bbbb48}{\text{ti}}\color{#cfb440}{\text{ng}}\color{#dea53b}{\text{ s}}\color{#e58e36}{\text{om}}\color{#e56e30}{\text{et}}\color{#df4828}{\text{hi}}\color{#da2121}{\text{ng}}[/math]

[math]\color{#781b86}{\text{I h}}\color{#671c94}{\text{ave}}\color{#571da2}{\text{ re}}\color{#4c23ae}{\text{fin}}\color{#462eb9}{\text{ed }}\color{#3f39c4}{\text{my }}\color{#3f47c8}{\text{rai}}\color{#3e55cd}{\text{nbo}}\color{#3f62cf}{\text{w c}}\color{#416fce}{\text{olo}}\color{#437ccc}{\text{rat}}\color{#4786c6}{\text{ion}}\color{#4b90bf}{\text{ al}}\color{#5098b7}{\text{gor}}\color{#56a0ae}{\text{ith}}\color{#5ba7a4}{\text{m t}}\color{#62ab99}{\text{o a}}\color{#6ab08f}{\text{cco}}\color{#71b484}{\text{mod}}\color{#7ab77a}{\text{ate}}\color{#82ba70}{\text{ st}}\color{#8cbb68}{\text{rin}}\color{#96bc5f}{\text{gs }}\color{#9fbd58}{\text{of }}\color{#a9bd52}{\text{muc}}\color{#b3bd4c}{\text{h l}}\color{#bcbb48}{\text{ong}}\color{#c6b844}{\text{er }}\color{#ceb541}{\text{len}}\color{#d5b03e}{\text{gth}}\color{#dcab3c}{\text{ at}}\color{#e0a23a}{\text{ th}}\color{#e39938}{\text{e c}}\color{#e58e35}{\text{ost}}\color{#e68033}{\text{ of}}\color{#e67330}{\text{ a }}\color{#e3632d}{\text{bit}}\color{#e1522a}{\text{ of}}\color{#de4227}{\text{ qu}}\color{#dc3124}{\text{ali}}\color{#da2121}{\text{ty}}[/math]

If f: [0, 1] → [0, 1] is a continuous function, how do I prove that there must exist a fixed point t for which f(t) = t? I know that [0, 1] is connected, and if g(t) = f(t) - t and no t exists so that g(t) = 0 then that probably would imply [0, 1] can be split up into two open sets, resulting in a contradiction. I just cant seem to fill in the details though.

Is there anyone who understands main/interaction effects in statistics?

We had a test recently in which we had to analyse two models on R to explain variation in a variable (petal length). One model explained petal length as a response to variation in petal width and flower species + interaction between the factors, while the other explained it purely as a product of variation in petal width.

The first model (Petal.Length~Petal.Width*Species) was significantly better because species had a significant effect on petal length and explained most of the variation. There was however no significant effect of Petal.Width:species interaction on the response variable.

The correct answer to a question in the test states that "Model 1 is better than Model 2 : the dependence of petall length on petal width varies by species"

Isn't this bullshit?
I mean it sounds like it's talking about an interaction effect to me in that answer because it's saying that the relationship between petal length and width varies by species which it doesn't. Petal length itself does vary between species INDEPENDENT of petal width though.

Can anyone help me

pls help a brainlet

just consider the function g(x) =f(x)- x. it is continuous and g(0)>=0, g(1)

just add 9 to every function and do the classic solid of rotation integrul integrul

i don't understand ;_;

the axis is at y=-9
to make things easier just translate it to y=0.

draw it

Imagine that you create a cylinder from revolving that region about -9

You can find the volume of infinitesimally small cylinders at a particular point and sum then to find the volume.

V = 2π(radius)(height) ; cross sectional area.

Find the radius and height

If a tautology is something that's true in all possible cases, how can we find a case where a disjunction 'p or not p' isn't a tautology, namely if three valued logic applies, and then still have people claiming it's a tautology? The mere possibility of it being wrong should stop it from universally obtaining. I must be missing something.

Well I'm willing to bet that the name of your advisor and school matter, but not to the point of making up for a lack of interesting work altogether.

en.wikipedia.org/wiki/Brouwer_fixed-point_theorem

taking algebraic topology next semester and two main topics are the ring structure of cohomology and the poincare duality theorem

i've found a handful of ring structures i want to get comfortable with computing, are there some important concepts i should check out that come through poincare duality?