/sci/ - Science & Math

>>9714560
Why do top scientists always have such messy offices and studies?

>>9714575
Being a top scientist usually means they are autistically devoted into that specific subject which increases the likelihood of them giving a shit about anything else, such as social life, clean room, healthy lifestyle, etc.

How do you make yourself study really hard without drugs?

>>9714585
Be devoted to the subject that you are learning. For me, I have to love what I'm doing. Freshman year I took a bio class and chem class and got B and B-. After that I took only math and cs courses which is considerably more difficult than bio and chem (real analysis and nonlinear optimization) and still aced it because I realized the joy of learning from those classes were actually fun. Got A's and A-'s on all my math and cs courses until right now in Junior year. It's all about being passionate about the subject you are learning

>>9714560
If statistics, probability, and neural networks exist, why don’t people use these resources to their advantage to calculate the odds of games to help them win sports bets?

>>9714600
How about without being passionate either?

>>9714613

they do

>>9714585
you won't believe me when i tell you this. but if you don't drink alcohol or smoke pot or take any drugs and quit consuming 200g of refined sugars, you will get your attention span back. coffee helps too.

>>9714651
But like really hard, like 8 hours a day + plus side projects hard

>>9714660
bump I really need to know this

>>9714660
With your current mindset, hell no. The only tools for studying hard are drugs, asian parents micromanaging, or good mindset. Just fail or do drugs. Embrace that you're a brainlet.

>>9714710
What drugs work?

>>9714710
how do I into mindset? Like discipline right? I try but I'm never able to study *that* hard.

Can someone explain to me how he found the variance for this.

>>9714734
Well, I found out how to do it using n*p*q, but I don't remember the prof ever teaching us that. Is there a way to do this using E[x^2] - m^2? n*p*q is easier, but I don't know why it works or anything like that.

>>9714727
any stimulants

>>9714734

thats a binomial distribution

variance of a binomial dist = np(1-p)

p = .5
n=20

.5*20(1-.5)=10(.5)=5

source: Math Major

CS brainlets

>>9714792
But which are the "best"

Someone help me, I'm begging you.

What is the ORDINARY generating function for m(x)^2, where m(x) is the Mobius function?

What about for |m(x)| ?

Answering either of these will go a long way for me.

How do we fix /sci/

Math, CS, and Japanese triple major here. Do you guys think it's acceptable to stretch this workload over 5 years instead of the normal 4? I'd really love to get all this shit done in 4, but looking at major requirements I'm not seeing many viable paths in under 4 years, even with Summer and Winter courses. It would've been possible if I didn't dick around for my first two semesters like a lazy fucking Freshman, but that boat's sailed.

>>9715007
Get rid of all people in pic related.

Why would I get vectors that are colinear with one another when using Gram-Schmidt to construct an orthonormal basis for a subspace of R^n? My matlab code looks right.

>>9715101
take the 5th year. you won’t regret another year in college as long as you like the school you’re at. you will always think what ifs if you drop a major you actually cared about

you will also regret cramming 20+ semester hours and tanking your GPA.

take the 5th year

>>9714816
amphetamines, methylphenidate, modafinil to a lesser extent
brand names respectively: adderall, ritalin, various names

>>9714560
shouldn't we have a medicine general? with the obvious disclaimers and shit. would you med/bio people help?
having a /med/ general would reduce the amount of threads...

>>9714585
you need a silent place, where no one will interrupt you.

can any medfags explain what my primary care physician meant when she said the infection that was draining on its own had "good tracking"

If I've only studied maths up to high school level, what would be good preparation for Zorich's Analysis?

Is a defining characteristic sufficient for a definition itself?

e.g.
What is a countably infinite set?
Defintition: A set is countably infinite if its elements can be put in one-to-one correspondence with the set of natural numbers.

Defining Characteristic: Any set such that each element will be reached in a finite number of terms when counted off in order.

Got into a debate with someone being pedantic and i was just curious if I was technically wrong or not.

>>9715309
Assumes the axiom if choice

>>9715309
For any set and any element in that set, there exists a well ordering of the set such that the element is reached in finite time

I don't see how that is relevant to the question

>>9715328
This is a nonsense reply, you have to "start counting" at a certain element for this to make sense, otherwise IR would be countable.

>>9715352
Well nonsense question, how do you count off something in order if it's not already in bijection with the naturals, unless you're already assuming that it is well ordered, in which case your defining characteristic is again the definition of the bijection with the naturals

>>9715360
Like literally, what do you think the word "count" means, you're using it very loosely but it's nontrivial to count things in infinite sets

>>9714560
That guy on the left looks annoying

>>9714660
Just sit down and study. As in, don’t get up until you are honestly satisfied. You’ll know when you feel exhausted that you’ve finally completed something you have been wanting to do for a long time.

Is it true that you might not need an MS to get a PhD?

>>9715550
yes, most math majors go for phd and not ms

>>9715550
You don't. Honestly the default is to go straight for the PhD. The main reason to get a Masters is because PhD programs care about your average GPA at your last schooling. That means if your GPA was not great in undergrad, you can get a Masters first and then get the PhD.

Since a Masters usually accelerates the PhD, you don't lose much time or money doing it. It's not a bad idea, honestly.

Okay, here are some brainlet questions about Force and Newton's laws of motion:

So the first law states that when the sum of force = 0, an object will either be at a standstill or moving in a straight line at a constant velocity. The third law states that for every force that is applied to an object, there exists another force of equal value pointed in the opposite direction. Doesn't this effectively mean that the sum of force is always 0? Let's say a square object's weight applies 10N downwards. There's then a force of 10N being applied upwards, and the sum is zero. We then apply another force to the side of the square of let's say 5N. There'll be a force of 5N counteracting that, so the sum is still 0 - is the object moving? What decides if it is? When is the sum of force actually not 0? And yes, I know full well I might be retarded because this is elementary stuff.

>>9715816
>Doesn't this effectively mean that the sum of force is always 0?
See the horse and cart problem: http://www.batesville.k12.in.us/Physics/PhyNet/Mechanics/Newton3/HorseAndCart2.html

>>9715829

Thanks, that's actually really helpful. I do physics as an autodidact, and my book doesn't actually do anything to explain anything like that.

If I remove the moldy part from a papaya, is it safe to eat the rest?

>>9716136
yes
go do it

What gre score for chemistry PhD?

>>9716136
No.

I'm trying to solve an equation of the form:

[math]a + \frac{b}{s^x + 1} + \frac{c}{t^x + 1} = 0[/math]

Obviously I want to solve for x. All the quantities are, or should be, real.

Wolfram Alpha seems able to spit out specific solutions (i.e. if I specify a,b,c,s,t), but won't give a general solution, nor is it possible (at least without Premium) to see its working.

I've tried implementing some basic numerical methods to solve this (Newton-Raphson etc.), but I keep encountering various instabilities (df/dx ~ 0) or other divergences, mainly due to not having much "a priori" knowledge about the function.

Pretty much the only property I'm sure of is that there's a discontinuity/singularity about x=0.

The only thing I haven't tried yet is a simple bracket-expansion scheme, which precommits to finding a solution on a particular "side" of x=0, and comparing [math]f(x=\pm \epsilon)[/math] with values progressively further from x=0, hoping to spot a sign change.

I had considered first trying to solve the simpler equation, in two variables:

[math]a + \frac{b}{S + 1} + \frac{c}{T + 1} = 0[/math]

for S and T, and then try to work out x from those, but I haven't thought through the details of how I'd do that yet.

Any suggestions or insight would be greatly appreciated.

(Background: this equation results from the expression before "which can be solved numerically ..." on https://en.wikipedia.org/wiki/Richardson_extrapolation , and you'll notice that the article doesn't go into any further details)

>>9716698
As a further clarification, s and t are both guaranteed to be real AND positive.

>>9716773
In fact, it might even be the case that both s and t are guaranteed to lie in (0,1]...

>>9714801
You don't need to rely on the binomial distribution to prove this. It's way more straightforward and generic to use that if X=Y+const then X and Y have the same variance (which I obvious and can be trivially proven if needed).

So I had this question yesterday, and I'm still confused on it. It's asking me to find the surface integral of the scalar function 2x + 2y + z^2, over the unit sphere using the Divergence Theorem. I believe the unit normal vector for the surface is <-sinΦcosθ, -sinΦsinθ, -cosΦ>, but I'm still not sure how to go about constructing the vector function from just this.

>>9716698
> Pretty much the only property I'm sure of is that there's a discontinuity/singularity about x=0.
There is a point of inflection at x=0. Each term is a sigmoid, and the function is anti-symmetric about (0,a+b+c)/2).

>>9717377
Does knowing it's two sigmoids help solve it in ant way? How did you reach the conclusion about antisymmetry (odd-ness)?

>>9717384
>>9717377
>>9716698
AARGH - I just realised I copied my original expression wrong from my whiteboard.

The "+1" expressions under the fractions should be "-1". Serves me right for late night mathsposting.

>>9717388
[math]a + \frac{b}{s^x - 1} + \frac{c}{t^x - 1} = 0[/math]

>>9715540
this

>>9714560
i have a physics exam tomorrow and im really under prepared. I understand the content taught easy and in depth.But for some reasons in exams find it really hard to do the questions, i think because its in a different context? anyway how do i live with myself failing and how do i hold back tears in an exam?

if atoms are neutrally charged, how come they're affected by electromagnetic waves?

>>9714613
Because results for previous games are perishable

>>9717117
Anybody at all?

>>9717117
What surface?

Why not use electrolysis to break down co2 on mars and make co+o2 in order to power rockets either for sample returns or various exploration by hopping? Is there scientific reason why such vehicle is impossible? I know efficiency will be lower but as known with hydrogen lessons in rocketry theoretical efficiency isn't everything.

I have an angle theta that I have worked out but it is not in the specified range. Can I simply add 2*pi or remove 2*pi until it is in that range?

>>9717729
The unit sphere

>>9717837
Oh you wrote it in the original, I somehow didn't see it.
You want to compute [math] \int_{\text{sphere}} f dA [/math] where f is the scalar function and dA is an infinitesimal area of the sphere.

First parametrize the unit sphere using spherical coordinates:
[math]
g:(\theta,\phi) \mapsto (\sin\phi \cos\theta, \sin\phi \sin\theta, \cos\phi)
[/math]
where θ from 0 to 2π, φ from 0 to π.

Now compute the infinitesimal region given a point on the sphere with coordinates computed given some θ,φ.
[math]
\lVert \frac{\partial g}{\partial\theta} \times \frac{\partial g}{\partial\phi} \rVert d\theta d\phi=\\
\sin\phi d\theta d\phi
[/math]
See why it is computed this way here:
https://math.stackexchange.com/a/131811

In those coordinates, f becomes:
[math]
2\sin\phi \cos\theta + 2\sin\phi \sin\theta + \sin^2\phi
[/math]

So, you have to compute this:
[math]
\int_{\phi=0}^{\pi} \int_{\theta=0}^{2\pi} (2\sin\phi \cos\theta + 2\sin\phi \sin\theta + \sin^2\phi) \sin\phi d\theta d\phi
[/math]

>>9717972
for f I meant to write
[math] 2\sin\phi \cos\theta + 2\sin\phi \sin\theta + \cos^2\phi [/math]

Do probiotic supplements actually do anything?

I expect whatever claims the manufacturer make are exaggerated either way, but wondering if there's solid data suggesting if they provide some marginal benefit, or if it's just total horse shit and the organisms will just die in your stomach anyway if they even survived on the shelf long enough to get consumed.

>>9717972
I still dont know how to use that with stokes theorem / divergencs theorem since I dont know how to make that a vector function I can take the divergence of

Can somebody give me a pointer on how to get started here? No idea how to model this using game theory - an investor basically has infinite strategies (i.e. amounts of money to invest), right? I tried plotting the two surfaces, but this just shows returns increasing towards infinity as A and B both increase their investments.

>>9718137
never done any game theory before so i dont really know what i'm talking about. but if you plot the vector field for those equations one of three things occurs:
-both tend to infinity;
-both tend to zero; or
-they tend to the point (34/5, 18/5)

not sure if any of that helps you.

>>9718002
Are you sure you are supposed to apply Stokes or Divergence on that? Cause it makes no sense.

>>9715816
The forces act on the opposing bodies. Think of billiard balls. When you strike the cue with some force, you can feel the stick shudder from the impact despite changing the momentum of the cue considerably. When the cue strikes a marked ball, it may transfer nearly all of its momentum to it. This is because in a nearly elastic collision, the stationary ball applies a monetary force to the momentous cue with nearly enough to stop it, or at least slow it considerably. However, the cue's force unto it will give it a new momentum.

Think it over.

>>9718371
momentary, not monetary

>>9718002
nigga just turn 2x+2y+z^2 into polar coordinates how hard can it be

I have a 2x2 matrix I'm trying to find the eigenvector for, but when I try to use elementary row operations, I cannot get the second row to be [0,0] because one of them is a non-zero constant and one of them is 0, so if you do a row operation to get the non-zero constant to 0. the other one is 0 +- something so it becomes non-zero. How do I get rid of them?

The matrix is: row 1=[0,-4], row 2=[-1,3]

>>9718529
Did you already calculate the eigenvalues?

>>9718570
Yeah, they were 2 and -1.

>>9718594
And did you subtract them from the matrix?

>>9718602
Yeah, I did N(lambda(I)-A)v=0. Its when I try to reduce it to row echelon form the trouble starts.

>>9718594
Maybe I am wrong, but my eigenvalues values are -1, 4.

Sorry if misguiding.

>>9718672
Just write down the initial matrix you're trying to solve.

>>9718284
>>9718483
Yeah the problem literally says to use the divergence theorem

>>9718672
>>9718685
Here's my working for eigenvalue.

>>9718699
you forgot a minus in front of the 4
[eqn]
\lambda^2-\lambda-6=0\\
\lambda_1=-2, \lambda_2=3\\
[/eqn]
Eigenvector for [math]\lambda_1[/math]:
[eqn]
\begin{pmatrix}
\lambda_1 -2 & -4 \\
-1 & \lambda_1 +1
\end{pmatrix}
\begin{pmatrix}
v_1 \\
v_2
\end{pmatrix}
=0\\
\rightarrow
\vec{v}=
\begin{pmatrix}
1\\
-1
\end{pmatrix}
[/eqn]

The second eigenvalue is analogue

>>9718695
Wait, maybe you meant to compute the integral of the scalar function on the Ball, not just its boundary (the sphere)?
If that's the case then you can use the vector valued function:
F(x,y,z)= (x^2,y^2,z^3/3)
which has divergence equal to f.
You can then proceed to compute the surface integral of F on the boundary of the ball (i.e. the sphere) which will be equal to the volume integral of f on the ball.

>>9718746
Thanks I got the same thing now you pointed that out. I think my brain kept covering up the mistake because I'd been working on it for so long. Fucking minuses and pluses, they seem to be the hardest thing about matrices.

>>9718685
> The matrix is: row 1=[0,-4], row 2=[-1,3]

But it seems to be evoluting

>>9718768
Don't worry about it, it was my fault that matrix was wrong because I forgot a minus.

>>9714651
I wonder does that N-back training work?

>>9715550
You can even get a straight MS in rare cases.

Suppose you have a sealed container floating around in space, filled with water at 10 C and 1 atm. What happens when the container is opened? I guess obviously the water would boil, but how rapidly? Would some of the water in the container freeze?

Is the language of mathematics legitimately well designed or is it just arbitrary historical bullshit?

>>9719177
the language of mathematics is pretty poorly designed considering the majority of objects are just named after the guy who popularized them

I've seen a few places the claim that quadratic reciprocity gives an easy algorithm to compute Legendre symbols, by repeatedly taking prime factorizations, reductions, and using reciprocity. However, isn't it easier to compute [math] \left( \frac{x}{p} \right) = x^{(p-1)/2} \pmod p [/math] directly by repeated squaring? From a computational standpoint, isn't this easier, since it doesn't require doing prime factorizations?

Besides being used for computing Legendre symbols, what would lead one to naturally think about quadratic reciprocity?

Best book for set theory?

>>9714600
harder than freshman chem, sure.
Harder than serious pchem, doubtful.

>>9715155
Explain to me how your pre-orthogonalized vectors, which are random integers between 1 and 4, are orthogonal

>>9719704
jech hrebaek or whatever for intro level, jech for advanced level

>>9719177
most of it is historical bullshit, but it usually helps to remember the stuff, and it lends itself to "abuse of notation". Parantheses ( , ) are used for sooo many different things it's ridiculous. Also there is always historical notation on everything, like the coefficients of the Weierstrass form of elliptic curves depending on if it's over the complex numbers or finite fields, etc

>>9719471
for p large, this becomes unfeasible for any x

at least from a pen and paper computation standpoint

I have a large whole number
How do I find a thing to divide it by to get the smallest whole number possible?

E.g. I got 1078, I want to divide it by something to make it as small a whole number as possible
Is there an easy way or do I just type 1078/2, 1078/4, 1078/6, 1078/... into my calculator?

I'm fucking dumb
Use case here is equations where I end up with shit like 452x + 894z = 654 (just an example these are random numbers I made up), I want to divide the whole equation by something to make it small

>>9720046
Nevermind I think I'm just being really stupid here
In the equations that shit would just divide itself when I try and get 1x or whateve
Nevermind

>>9720046
>E.g. I got 1078, I want to divide it by something to make it as small a whole number as possible
Divide it by 1078

>Use case here is equations where I end up with shit like 452x + 894z = 654 (just an example these are random numbers I made up), I want to divide the whole equation by something to make it small
It's called greatest common denominator (or gcd)

>>9720046
>Use case here is equations where I end up with shit like 452x + 894z = 654 (just an example these are random numbers I made up), I want to divide the whole equation by something to make it small
There is no easy way, you still end up doing divisions

Is this a copy editing mistake by Axler?

3rd Edition Linear Algebra Done Right, section 3.F problem 26.

Suppose [math] V [/math] is finite-dimensional and [math] \Gamma [/math] is a subspace of [math] V' [/math]. Show that

[eqn] \Gamma = \{ v \in V : \varphi(v) = 0 \text{ for every } \varphi \in \Gamma \}^{0} [/eqn]

That should be [math]\Gamma = \{ v \in V : \varphi(v) = 0 \text{ for every } \varphi \in \Gamma^{0} \} [/math] right? Because the annihilator for a vector does not make much sense.

>>9720128
I'm an idiot, that set is a set of operators which is what I want. Forget it.

>>9714560
integrate [math] \int \frac{ln(x + 1)}{(x + 1)^3} dx [/math] via u-sub, no by parts faggotry allowed, if you cant, youre a brainlet and should off yourself.

>>9720262
Do your own homework.

>>9720262
somebody would have told you what to do if you didn't post like such an asshat

>>9720263
>>9720274
i know what to do retards, just testing /sci/ (shitposting badly).
now seriously, doing that with a usub is a fun challenge.

>>9720262
>no by parts faggotry allowed
Why impose random conditions like this?

how hard is it to become a professor at a uni in a foreign country? assume my degree is from the US in a top 10 uni in my field and the uni is in a country outside the US and UK, but I am fluent enough in the language

What trend line should I draw here?

y = a * e^b(x - c) with total least squares/deming/perpendicular distance regression?

>>9720262
[math] u ={ 1 + 2 \ln(x+1) \over 4(1+x)^2} [/math], du = integrand

>>9720912
Here's a rollercoaster ! You're welcome, Anon :)

>>9714560

Lads I'm going to either pure physics or pure chemistry next year. Will I get to work on nanomachines in both cases? I really wanna make fucking nanomachines, which harden in response to physical trauma.

>>9720970
Please do not contribute to the rise of the machines, Anon.

>>9714575
>messy offices and studies
This picture is nothing, anon. I've seen way worse. If anything, it looks surprisingly clean.

Is it worth it to retake a class I got a C in just for GPA? Before this semester (jr year, 2nd semesterl) I had a 3.9 GPA, and now after it will probably be 3.76-3.8 as I really shit the bed and just skipped and procrastinated the whole time. It is in an EE probability course that is required for the major, but not related to my focus (optics, photonics) and believe I could get an easy A if I take it again. Am i fucked for MS/Phd applications next semester?

>>9721021
Also if I take the course again I may have to take another semester to graduate, but I could possibly get more research/internship experience before applying to grad schools I guess.

>>9714560

Whoa that was my professor at stony brook, I think

Need help with this.
Posted on wsr but no replies.

how to learn solidworks and CAD in two weeks?

just got a D on linear algebra 1 final

>>9721125
proff is a cuck

>>9721125
>just got a D on linear algebra 1 final
are u in middle scool? wtf is this?

How can I become strong?

>>9721315
>>/fit/ welcomes you anon

List all the group homomorphisms Y : Z42 → Z24 and determine the kernel and the image of each group homomorphism (express the kern and img as Zn for appropriate n)

>>9721381
A homomorphism out of a cyclic group is determined completely by where the generator maps. Your options are exactly the elements of order dividing 42.

How do I remember so many formulas?

>>9721125
You didn't even have to prove anything?

I'm probably an idiot who is incapable of understanding physics. How the hell do step up transformers work? How can you just 'get' more voltage?

>>9721702
Wait is it to do with magnets and coils and shit? Fucking magnets, what even are they.

>>9721125
>>9721128
the fact that he gave you points at all for those shitty unreadable answers really does say the prof is a cuck to the system, but it mostly says you are a retard

I have a vector field that I want to prove conservative.
So I thought about the component test.
the problem is that one of the components of the vector field is has the term x/y in it which makes me think the vector fields domain is not simply connected. Hopefully the good news is that the partials do not equal eachother which imply that there is no potential function f such that F = [math] \nabla [/math] f.
are my reasoning's and assumptions correct?

>>9721935
Never mind I'm a brainlet I was reading the proof in the book wrong it says "Proof that Equations (2) hold if F is conservative"
where the equations are partials in the component test. So if the equations do not hold F cannot be conservative.
It turns out that D only needs to be simply connected to for the partial derivative equations to imply that F is conservative

>>9721054
Sorry for messiness been a while since I did physics. Also what oscillations? We're missing some context

is this is valid way to substitute variables?
[math]n^{k+2} + m^{k+2} = 31p[/math]
[math]n^{k+3} +m^{k+3} = 31q[/math]
[math]n * n^{k+2} + m^{k+2}*m[/math]
[math]n * 31p * m[/math] (the substitution)

>>9722029
no, because multiplication goes first
Consider

3+4 = 7
2*3+4*5 = 26

Can I get an object so high above earth surface it will contain so much potential energy it will collapse into a black hole?

>>9722032
so would it work if i used brackets?

>>9722083
nvm

>>9721963
oscilations come from solving equation of motion for particle b, and they only happen if particle has different charge than Q.

How is mathematics applied in the social sciences - not necessarily economics, but fields like government, sociology and psychology? Is it just stats, or is there more involved in "mathematical modelling"?

>>9721963
Forgot to say that an electron is released on the field.
Youre supposed to find the oscilations of the electron.
These are the provided answers.

>>9721028
someone help a brainlet out

>>9722065
No. Potential energy is the integral of force wrt distance. The force decreases following an inverse square law, so the integral to infinity is finite (that's where escape velocity comes from).

>>9721125
>>9721125
no you didn't: warosu.org/sci/thread/S9527179#p9535238
the only wrong on the professors part is that he gave you more than 3 marks for three vague statements and no proof

>>9722090
If you're not going to give me the correct question with everything included, like the signs of the charges, I'm not going to help you

>>9722189
Thats not me, butbI already provides that dude.
On the first pic the graph shows the charges.
The Q charges both have the same magnitude and polarity.
What else do you need to know?
Tell me and ill post

>>9721125
You need to learn how to prove stuff. What you wrote in the exams are not proofs.
You did someting analogous to:
>every number is a prime number
>proof: 11 is a prime number

Not sure if typo or if I'm just very dumb. The cross-sectional area can't be cm^3?

How can probability have an irrational value?

>>9722622
what's the probability that I hit the interval [0,1/pi] if i randomly throw a dart (without missing) at the interval [0,1]?

How ami suposed to know the roots of
x^2+x*(1-i)+2-2i
??
I tried using Bhaskara formulae but cant solve (6i-8)^(1/2) and cant use Rational root theorem cause i dont know what are the divisors of 2-2i

>>9722810
https://en.wikipedia.org/wiki/Quadratic_formula

>>9722840
>i tried using quadratic formula but cant solve (6i-8)^(1/2)
>try using quadratic formula
lol

>>9722227
Typo. Cm^2. Go ahead.

Is it worth delaying graduation by one semester (spring -> fall) and grad school applications by a year (start 2020 rather than 2019) just to get a better chance to get into a PhD program? I am in EE and have a scholarship for full tuition, so room+food would only be $5k at most for the extra semester, but I would then have 3+ semesters of research experience when applying rather than 1 semester experience. I also would do research or an internship in the summer of 2019 and 2020 (right before grad school) which I believe would help down the road as well. is my idea stupid or is it worth it?

[math]
-\frac{1}{p+5}
[/math]

p cannot be equal +/-5 or just -5?

>>9722983
the bottom can't be equal to 0 so p cannot be equal to -5

>>9722983
Do you know why it can't be -5?

>>9722810
never mind, i finally fount the soution for (6i-8)^(1/2) being 3-1

>>9722990
and if I give context - see pic

>>9722991
yes, but see context

[math]
\frac{-1 * (p-5)}{(p-5)(p+5)} = - \frac{(p^2 - 5p + 25)}{(p+5)(p^2 - 5p + 25)}
[/math]

we are talking about identical relation here.

Reminder:

[math]
\frac{x(x-1)}{(x-2)(x-2)} = \frac{x}{x-2}
[/math]
^ identity, but x != 1;2

>>9722999
quickfix:
(x−2)(x−1) in the denominator of the example

>>9722810
> cant solve (6i-8)^(1/2)
6:8:10 triangle
|z|=10 => sqrt(|z|)=sqrt(10)
sin(arg(z))=3/5
cos(arg(z))=-4/5
sin(arg(z)/2) = sqrt((1-cos(arg(z)))/2) = sqrt(9/10) = 3/sqrt(10)
cos(arg(z)/2) = sqrt((1+cos(arg(z))/2) = sqrt(1/10) = 1/sqrt(10)

sqrt(z) = sqrt(|z|)*(cos(arg(z)/2)+i*sin(arg(z)/2))
= 1+3i

i need big help bros. please.

>>9723094
please

>>9723094
What have you tried?

>>9723124
not sure how to start. i think I would require the marginal distributions for both the mean and variance. then i would use some combination of the factorization criterion and the fact that its an exponential family distribution to obtain the sufficient and complete statistic.

>>9723124
i guess i would need the joint distribution given the mean and the variance?

How precise is an Electroencephalography? Could you use it to reliable control something complicated with your mind through it? How hard would it be to set such a thing up yourself?
I have enough programming skills, I'm just talking about the physics behind it, like calibration and stuff, how precise can the thing get? Can you build one by yourself? Or do you need to buy one to get any kind of precise measurements?

I want to connect a USB stick and learn to save and retrieve memories on there with my brain, I could write simplified drivers to make the interfacing easier, but I need a connection to my brain. No surgery though.

Are my titration calculations correct?

NaOH + AgNO3 -> NaNO3 + AgOH

So stoichiometry factor is just 1.

If I need to know how much NaNO3 I made, with the following info:

Conc. AgNO3: 0.5 Molar
Vol of AgNO3 in beaker: 0.02L
Vol of NaOH in burette that I titrated: 0.03L

To find the number of moles of NaOH at the end point of the titration, shouldn't that just be the number of moles in 0.02L of 0.5Molar AgNo3?
So: Moles = Molarity/L
= 0.5 Molar/0.02L
= 25 Moles
Therefore there was 25 moles of NaOH in the 0.03L I titrated.

Or should I have been utilising the C1*V1=C2*V2 equation?

Wait sorry, I don't want to know how much NaNO3 I made.
I just need to know how many moles of NaOH was used to get to the end point

>>9723374
>Could you use it to reliable control something complicated with your mind through it?
Yes, depending on how "complicated" you're getting. There have been a lot of projects to fly drones with BCI. More complex things typically require invasive implants that they'll only put in if you're horribly disabled.

>How hard would it be to set such a thing up yourself?
The cost is more of a barrier than the difficulty.

>I want to connect a USB stick and learn to save and retrieve memories on there with my brain,
That's a totally different question if you mean literally taking memories out of your brain and putting them back in later.

>>9722799
are there complex probabilities?

>>9723678
No, but there's this:
https://en.wikipedia.org/wiki/Complex_measure

>>9714584

I have always thought people that know too much are actual autists.. just attend to a talk of a top physicist and you will realize that

My only career choice at this point is either acadamic work in Math or hamburger engineer at Mcdonalds

Given my average grades of B in 2nd year how likely am I to get a Maths job (other than a high school math teacher)

>>9724035
>hamburger engineer at Mcdonalds
What the problem here?
Advantages are: free food

I recently got my bachelor's in EE but I didn't do any interships while studying. How fucked am I for getting a job in my field? I have been applying and hearing only negative responses, some mentioning my lack of experience as a reason. Is there any way to fix my situation?

I have no idea how to approach this. I know U(147) is just the elements coprime to 147 so part a would be relatively simple, but I am not sure about part b-d when determining an isomorphism classes

>>9724128
so a would just be φ(147)=84 where phi is the euler-phi function (and the answer is given in following question)

>>9724128
[math]441 = 3^2 \cdot 7^2[/math]. An Abelian group of order 441 is a product of cyclic factors d_1 | d_2 | ... | d_n. Only [math]{\bf Z}/(441)[/math] and [math]{\bf Z}/(3) \times {\bf Z}/(147)[/math] contain any elements of order 147.

>>9724147
thank you

Is there something beyond complex numbers?

>>9724287
You can perform essentially the same extension from R to C as many times as you like, doubling the dimension over R each time.
After the Complex numbers come the Quaternions and after those are the Octonions.
After that are Sedenions but nobody gives a shit at this point because there's so little structure left and the numbers are so cumbersome that there's nothing interesting here.

>>9724301
>>9724287
reals to complex you lose linear order, complex to quaternions you lose commutativity, quaternions to octonions you lose associativity, octonions to sedenions you lose being an integral domain, and at this point you might as well stop

>>9724428
Do ternions exist?

>>9724432
no, and actually, this question is what hamilton pondered for like 15 years before discovering the quaternions

>>9724433
a "no" does not really satisfy me... where can I read about that?

>>9724447
Well, depends on what algebraic structure you want on your "ternions". The structure you're probably looking for is that of an "algebra over the reals". Algebras are basically vector spaces where you can also multiply elements, on top of being able to multiply by scalars and add them. In this case, the most interesting type of algebra are real division algebras, that is, algebras where you can also do division in some sense. The complex, quaternions and octonions are all real division algebras. Adams and Atiyah proved that all real division algebras need to be vector spaces of the reals of dimension 2^n, with n=1,2,4,8, using K-theory and topological methods. However, not all division algebras are isomorphic. You can further refine what you want, for example, there are theorems by Hurwitz, Frobenius and Zorn that say all associative real division algebras must be [math]\mathbb R,\mathbb C,\mathbb H[/math], all alternative (which is weaker than associative) must also include [math]\mathbb O[/math], all normed algebras must be all the aforementioned ones, etc

>>9724462
thanks, I was asking because of ternary logic but it seems the connection I hoped to find is not there.

What you wrote is beyond my understanding but I am currently studying vector spaces so I will keep your post in mind, thanks again.

Turbo brainlet here, how do i get from the firs two equations to the third ?

[eqn]
tan\phi =-\frac{\Omega r}{k-m \Omega ^2}

\\
\\

(-m \Omega^2\cos{\phi}- r\Omega \sin\phi +k \cos\phi)c_{1} =F_{0}

\\\\
c_{1}=\frac{{F_{0}}}{\sqrt{(k-m \Omega^2)^2+(\Omega r)^2}}
[\eqn]

Turbo brainlet here, how do i get from the firs two equations to the third ?

[math]
tan\phi =-\frac{\Omega r}{k-m \Omega ^2}

\\
\\

(-m \Omega^2\cos{\phi}- r\Omega \sin\phi +k \cos\phi)c_{1} =F_{0}

\\\\
c_{1}=\frac{{F_{0}}}{\sqrt{(k-m \Omega^2)^2+(\Omega r)^2}}

[eqn]
tan\phi =-\frac{\Omega r}{k-m \Omega ^2}

\\
\\

(-m \Omega^2\cos{\phi}- r\Omega \sin\phi +k \cos\phi)c_{1} =F_{0}

\\\\
c_{1}=\frac{{F_{0}}}{\sqrt{(k-m \Omega^2)^2+(\Omega r)^2}}

How do i get from the first two equations to the third?
[eqn]

tan\phi =-\frac{\Omega r}{k-m \Omega ^2}

\\
\\

(-m \Omega^2\cos{\phi}- r\Omega \sin\phi +k \cos\phi)c_{1} =F_{0}

\\\\
c_{1}=\frac{{F_{0}}}{\sqrt{(k-m \Omega^2)^2+(\Omega r)^2}}

[/eqn]

>>9724707
[math] \begin{align}(-m \Omega^2\cos{\phi}- r\Omega \sin\phi +k \cos\phi)c_{1} &=F_{0}\,;\\ c_1&=\frac{F_0}{-m \Omega^2\cos{\phi}- r\Omega \sin\phi +k \cos\phi}\\&=\frac{F_0}{\cos\phi(k-m\Omega^2 )- r\Omega \sin\phi}\\&=\frac{F_0}{(k-m\Omega^2)^2+(\Omega r^2)} \end{align} [/math]
fuck knows how the [math] \sqrt{\cdot} [/math] comes into it

How do you know when a girl likes you?

>>9724848
It doesn't matter. Ask her out and if she rejects you, move on, playboy.

>>9724722
maybe you missed a square root in the expression for c_1??

>>9724848
if u no u no

>>9724936
mhh no I didn't, also how what did he do in the last step? How did he remove [math]sin \phi[/math] and [math]cos \phi[/math]

>>9724950
tan phi = sin phi / cos phi

now note that your expression for tan phi is already a fraction..

Question: given y= -x^2 parabolic function why is that Ymin on the x range (-3;2] (exclusive -3, inclusive 2)
is -4 (i.e. it exist)
but
if we take y= x^2 with x range [-0,3; +inf) (inclusive -0.3, exclusive +infinity) then Ymax cannot be defined

Shouldnt be Ymax be 0.09 as per the logic in first example because only -0.3 is an inclusive part and infinity is exclusive? Same logic was used to define -4 being Ymin in first example, where -9 was exclusive.

>>9724962
Still not getting it, forgive my brainletness

where did I fuck up

[math]
x^2 = -2x - 1;

x^2 + 2x = -1;

x(x+2) = -1;

x+2 = -\frac{1}{x} = -1 * (\frac{1}{x});

2 = -\frac{1}{x} - x = -1 * (\frac{1}{x} + x ) = -1 * (\frac{1}{x} + \frac{x}{1} ) ;

2 = - \frac{1+x^2}{x} ;

2x = -1 + x^2 ;
[/math]
wait what

>>9724987
Draw a right angled triangle with one angle being phi. What is tan phi? It is opposite / adjacent. in your pic, tan phi is already a fraction, so assign the numerator as opposite and denominator as adjacent. By pythagoras, calculate the hypotenuse. Now you can calculate sin phi and cos phi as the ratios that they are

>>9724970
your first example is wrong. There is no minimum, and 4 is certainly not the minimum - take for example x = -2.5

Your second example is correct, there is no maximum. Suppose x takes a maximum value, that is y is maximal. Then take an x a bit more to the right in the interval, is it bigger? Can you replicate this for every x in the interval?

>>9725013
on the very last step
2= -(1+x^2)/x
so
2x = -(1+x^2) = -1-x^2

>>9725024
>your first example is wrong. There is no minimum, and 4 is certainly not the minimum - take for example x = -2.5
Thanks let me provide a little bit context:
"Using the marked part of graph for function y = -x^2. find Ymin and Ymax and specify, to which X range it belongs."

The proper answer for this is Ymax = 0 and Ymin = -4

I assume it is incorrect because according to marked part the exclusive threshold function value is < the inclusive function value

>>9725027
Why?
let's assume 1+x^2 = z
then 2 = -z/x
[math]
2 = - \frac{z}{x}
[/math]
because
[math]
\frac{-a}{b} = - \frac{a}{b}
[/math]
therefore
[math]
2 = - \frac{z}{x} = - \frac{1+x^2}{x}
[/math]

>>9725035
the answer is wrong, as i said, there is no minimum. If anything -4 is a "critical value" although i doubt you've looked over those. Regardless, you can see that a minimum does not exist since you can never reach -3, that is, -3 is not in your interval, but every number before -3 is, and they take increasingly smaller values. If you take a number close to -3, there will always exist a number that is closer, so a minimum cannot be attained

>>9725041
Yeah, it just bugged me since answer didnt make sense so i needed confirmation. Thanks man

Any of you intellectuals have an idea ?

>>9725043
a proper answer to this you will find if you decide to study real analysis and/or topology in the future. They are purely topological arguments that go into it. That is, you can deform continuously your domain and still get the same answer. Maybe one day anon :^)

>>9725047
literally apply the definition of charge in terms of current you fucking retard

>>9725051
elaborate

>>9725056
literally google charge current time

don't reply to my posts ever again faggot

>>9725060
i'm sorry

>>9725064
apology accepted, sorry bro didnt mean to be mean :(

And follow-up question: how do I prove that y = -x^2 and y= x+5 do or do not intersect and at which points?

I understand that y= -x^2 is a parabola along the -y axis with max value of 0 and y = x+5 is a linear function y= kx+b, rising, with shift by Y to +5 so they never can intersect but how d oi prove it mathematically?

I end up with retarded shit like
x^2 + x + 5 = 0 which I can find a way to solve without using advanced quadratic formulas that not supposed to be available to me

>>9725070
the only way to solve it "mathematically" is doing what you did, that is, you have that y = -x^2 and y=x+5. Putting y = y, you get that x^2+x+5=0. Putting it into the quadratic formula, you get a square root of a negative number, therefore, there is no solution. They only other method that i know uses calculus.

>>9725079
> They only other method that i know uses calculus.
What do you mean by that?

3rd method would be graphical of course, but you cant use it for big values because it is imprevise

>>9725084
graphical is not a valid method of proof in high level math, although it is a very intuitive way to gain understanding. Using calculus, you can calculate the minimum and maximum values, and use the fact that a curve is decreasing while the other has constant slope, etc

>>9725091
fair enough

>>9714560
well ladS??

>>9725105
kill yourself braindead frenchfag

>>9725111

>>9725111
can you please just tell me the answer i will send you nudes of my girlfriend

>>9725116
do you want the answer or the explanation? i dont care about your ugly ass girl friend

>>9725117
Both please :( i swear i will never post on here again

>>9725118
jesus dude im just in a shit mood ok? chill

Ok in a series circuit, current doesnt divide. So the first pair of resistors, the 100 resistor and the second pair of resistors each get the same current. In particular, 100 has the largest current through it, since the parallel circuits divide up the current. Now, current likes flowing through the easiest path, and will divide itself in a proportional ratio. Hence, the first pair will divide the current into 2:1, and the second pair into 5:50. In particular, the least amount of current wants to go through the 50 resistor

>>9725125
Thanks my dude, whatever it is i hope your mood gets better

>>9725125
what a gentleman, everyone should take an example of you

>trying to tackle uni problems
>usually these are not that difficult, but you still struggle
>ask a question on math stackexchange and it gets solved in few hours thoroughly
>feel like a fucking retard and want to kill kys myself

What do, /sci/?

>>9715101
>triple major

How the fuck?

dont know if this is more /g/ oriented, but i'll ask here anyway

suppose x is a node in a binary search tree. then define left(x) to be the node in the left subtree of x and define right(x) similarly. are these two functions well-defined? iirc i was told yes, but i dont know how to prove it

Should I get an AA/AS in Math/Physical Science?
I've completed all the necessary classes, but the only thing stopping me is a fitness class. I could take one,
Is it worth having or should I just ignore it? I'm currently enrolled as an EE student.

>>9719743
pre-orthoganalized as in they haven't been orthoganalized yet

Which is leading? emf or VL?

>>9725335

>>9723636
Yeah no surgery sadly, not stupid or skilled enough to do it myself, and paying for it is just ridiculous.
I mean training myself to interface with the usb stick, which would mean I would be able to store information in there from my brain. Just like neurons start connecting to each other in children to get better at remembering things, After enough time I would have connections between my neurons to send the right signals to a very simplified USB mass storage driver to write and read information from it.
Or maybe fuck USB it seems like a bad idea, something like RAM would be better because of the parallel interface.

someone make a new thread

Why is the trig part of a precalc class so much easier than the first half?

>>9714585
drink lots of water.
eat a steady diet of vegetables and fruit, mostly.
stop eating shit with sugar in it (refined sugar).
get regular exercise, just walking can be it.
avoid drugs and alcohol.

>>9715101
what legit university allows a triple major?

How do you prove that the summation from n = 1 to infinity of 4^n / (3^n + 9^n) converges? I'm trying to use the comparison test to a geometric series but it's not working.

>>9726170
>I'm trying to use the comparison test to a geometric series but it's not working.
Why not?

>>9726176
Because 4^n/(3^n+9^n)<4^n/(3^n+3^n) but this doesn't tell us anything since the right hand term is divergent

>>9726194
>Because 4^n/(3^n+9^n)<4^n/(3^n+3^n) but this doesn't tell us anything since the right hand term is divergent
Why would you compare it to something divergent?

>>9726198

The other option I see
4^n/(3^n+9^n)>4^n/(9^n+9^n)

>>9725648
still 60+ replies before bump limit

>>9726199
>The other option I see
Nigga, what about 4^n/(3^n + 9^n) < 4^n/9^n

>>9726222
wtf im dumb idiot stupid stupid dumb dumb

>>9726170

>>9726226
It's okay anon, happens to the best of us

>>9726170
[eqn]\frac{4^n}{3^{n}+9^{n}}\leq{\left(\frac{4}{9}\right)}^{n}[/eqn] and [math]\frac{4}{9}<1[/math].

You're familiar with this theorem, yes?

>>9726228
oops i made a mistake because i read your other reply

but i guess you already know what it is
disregard this

>>9726230
Yeah, I don't know why I didn't just ignore the 3

>>9725176
Well-defined just means that one input, or in this case, one node won't map to two distinct places. Think about it: are there two left sub-trees? Or is there just one? If left(x) wasn't well-defined, you'd have more than one left subtree... which is nonsensical because you're in a binary tree.

>>9725146
Don't quit

>>9725039
>>9725027
>>9725013
bump

Help, is there an uncountable family of uncountable subsets if the irrational numbers, such that each subsey is compact and they are pairwise disjoint?

>>9726277
see >>9725027

>>9726310
no, as I said: >>9725039
nothing iswrong

>>9726314
>no, as I said: >>9725039
>nothing iswrong
What does that have to do with my post? You basically did 2 = -(a+b)/c, multiplied by both sides by c and got 2c=-a+b instead of 2c=-(a+b) because you dropped the parentheses for no reason.

>>9726289
>Help, is there an uncountable family of uncountable subsets if the irrational numbers, such that each subsey is compact and they are pairwise disjoint?
Compact with respect to which topology?

Writing proofs right now and I'm unsure what level of detail would I go down to

What's a good rule to follow

>>9726327
like I'm not sure what kind of things I can declare as too trivial to prove

>>9726327
>What's a good rule to follow
Enough detail for a classmate to understand

Medical question. How does constantly sucking in ones gut affect health and developmental outcome during puberty? From what I've read it can cause digestive problems and weak glutes/hamstrings, but I'm wondering if it can also effect development of the genitals and possibly the release of testosterone from the testes. If you suck your gut in now you'll notice that your flaccid penis shrinks as blood flow is restricted and the testicles retract to a position closer to the body which I suppose also damages spermatozoa. If you know much about physiology it would be helpful if you could clear this up.

>>9726323
The real.

Any Eurofags on? Im an amerilard thinking of doing my PhD (electrical engineering) in Europe just for the experience and if I like it might stick along for citizenship, but need to figure out which countries to pick. I was mostly thinking Germany, Switzerland, or (Northern) Italy as I am fluent in english, and maybe A2 to B1 in German and Italian. The position just requires english so I can just learn the second language on the side anyways. Which one would you eurofags choose assuming I get into any uni I apply to?
>inb4 fuck off we're full
Im ready

>>9726632
why not UK?

>>9726632
dont forget germans dont like hearing and speaking english, so you have to speak the language good enough that you dont need to use english words every few seconds because you dont know how to say something in german

>>9726700
I like the UK and they have great unis but they arent EU and I would want to learn a new language during the PhD which would be harder or less practical in the UK. I might apply to a few in the UK still though.
>>9726705
I think I should be able to get good with it after a year or two. How bad do they hate it? I had a few professors from Germany at my uni (US) and they had to ask some english words but it isnt really annoying or anything

Is it incorrect to write [math]W=\oint_a^b \textbf{F}\cdot\textbf{T}\,dt=\oint_a^b \textbf{F}\cdot \frac{d\textbf{r}}{dt}\,dt[/math]?
My textbook has [math]\oint_{t=a}^{t=b} \textbf{F}\cdot\textbf{T}\,ds[/math] for the first part. does it have to be ds or can you just say that the vector field and tangent vector are defined as functions of t?

are the math books on openstax.org good for refreshing fundamentals and learning / re-learning math?

>>9726740
second line
[math] \oint_{t=a}^{t=b}\textbf{F}\cdot\textbf{T}\,ds [/math]

>>9726730
not sure, but better dont borrow english words, instead try to ask for the word you are looking for (or just use simpler words), they are very proud of their language and literature
similar thing with italy, but you should get away with borrowing ((simple)) words
https://www.ef.pl/epi/regions/europe/italy/

>>9726740
It's just notation denoting unrigorous bullcrap.
The work of a path r inside a vector field F is computed this way:

Take an "infinitesimal" portion of the path r and call it dr (it is r(t+h)-r(t) where h is "very small").

At this place (r(t)), break F (i.e.F(r(t)) into two components, one along dr and on perpendicular to dr.
The component that is perpendicular to dr "contributes no work".
The component along dr "contributes work".
How much work does it contribute?
By definition, it contributes:
[length of component along dr] times [length of dr]
and you put a "-" if the component is pointing at the opposite way dr does
The above is equal the inner product of F and dr.

To get the Work, "sum" (integrate) all those infinitesimal works along the entire path r.
[math] \int_{\text{all of } r} F \cdot dr = \int_{a}^{b} F(r(t)) \cdot \frac{dr}{dt} dt [/math]

So, if T means dr/dt, then yes, the symbolism of your textbook is incorrect. (ds means dr your textbook)

Why does the integral from 0 to 2pi (rho hat * dphi) = 0?

>>9726928
>tfw u walked 360 degrees and walk away

>>9726969
Please explain. I am a brainlet but I know it's due to symmetry.

>>9726791
>(ds means dr your textbook)
What? no. s is arclength, r is the position vector, probably should've said that

X-ray penetration depends on material atomic number. Does it also depends on material thickness?

Example: I am standing in front of a plastic wall thick 1meter and then a plastic wall thick 10 meters. Will my dose be lower? (I realize dose will be lower because distance from x-ray source is much greater, but does plastic wall change anything?)

>>9726982
how about draw a picture and try to explain what you think should happen

how do i prove (ii)?

>>9727269
>how do i prove (ii)?
What have you tried?

What base would work? NaOH?

>>9727347
i think i have a proof, but i'm not really sure if it's correct:
Suppose [math] f(X)\in\ker\theta [/math]. Then [math] \theta(f(X))=[f(0)]_3=[0]_3 [/math]. Hence [math] f(0)=0+x [/math], with [math] x\in 3\mathbb{Z} [/math].
By the division theorem there exists [math] r(X),q(X)\in\mathbb{Z}[X] [/math] such that [math] f(X)=(aX+3b)q(X)+r(X) [/math], with [math] r(X)=0 [/math] or [math] \deg(r(X))<1 [/math] (so [math] r(X)=c [/math]).
So [math] \theta((aX+3b)q(X)+r(X))=[3bq(0)+c]_3=[0]_3 [/math]. Then [math] 3bq(0)+c=x [/math] and hence [math] 3|c [/math].
therefore
[eqn] \begin{align} f(X)&=(aX+3b)q(X)+3d\\&=aq(X)X+3(bq(X)+d) \,,\end{align} [/eqn] with [math] d\in\mathbb{Z} [/math]. So [math] f(X)\in\langle X,3\rangle [/math] and [math] \ker\theta\subseteq\langle X,3\rangle [/math]. The result follows from the above question he above question

>>9727350
NaOH http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch20/ch20-3-3-1.html

>>9727380
>http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch20/ch20-3-3-1.html
Yes but would the NaOH not also hydrolyse the left ester?

>>9727218
Yes because the light will disperse more from shit like Rayleigh scattering beers law etc

>>9714560
who's this dude, I see his pictures a lot here

>>9727459
Sam Hyde

>>9727459
idk but i imagine it ends with "stein"

>>9727356
>>9727356
why would this be wrong?

>>9726928
>>9726982
wtf does rho hat represent in the first place?

>>9727526
idk. im not that confident with it and didnt know if i'd made a mistake. does it look okay to you then?

starting to get into basic at home experiments, more specifically pyrotechnics but one thing I'm struggling with is finding sort of "chemistry sets" on amazon, it's all aimed at kids what do i search to find a set that includes the basics, i.e beakers, test tubes holders etc because now I'm wanting to move onto stuff that's more than just buying powders mixing them and igniting them also what're some good youtube channels that do at home project but focus on the science rather than just what you do?

>>9726705
sounds like you have never been to germany

What is the volume of .1095M HClO4 can be neutralized by 21.38g of solid CaCO3?

Is it 0 because the solvent is a solid?

I'm emitting 365nm UV light from a Nichia onto orange highlighter through these ANSI Z87+ goggles and it floresces.

What the fuck?

>>9728017
Same anon. The lens is polycarbonate so it should in theory block UV.

>>9715155
I assume you've figured this out by now, but you are supposed to subtract the projection of basis onto vector FROM BASIS, not from vector.
You are taking vector, and then subtracting the part of basis that is parallel to it. So of course the results are colinear.


clear all

coords = rand(5,4)
barycenter = mean(coords, 1)

vectors = coords-barycenter

vector=vectors(1, :)

basis1 = rand(4,1)'
basis2 = rand(4,1)'

basis1 = basis1 - ((dot(vector,basis1) / dot(vector, vector)) * vector)
basis2 = basis2 - ((dot(vector, basis2) / dot(vector, vector)) * vector) - ((dot(basis1, basis2) / dot(basis1, basis1)) * basis1)

dot(vector, basis1) / (norm(vector) * norm(basis1))
dot(vector, basis2) / (norm(vector) * norm(basis2))
dot(basis1, basis2) / (norm(basis1) * norm(basis2))

%ans = -1.6003e-16
%ans = 3.6209e-16
%ans = -5.3223e-17

>>9714585
Stop looking for tricks, including motivation. Instead, build discipline and hone your focus. Be a man, not a child

What's a good way to calculate the probability of dependent events? Why is probability so hard?

>>9727565
yeah

>>9714575
some people actually work

I have a linear differential equation and its Green function. I know the domain and the boundary conditions and everything.
How do I use the Green function to find the solution?

I understand I do an integral to find the contribution from all the x' at some x, but what are the limits of my integral? The Green function has a Heaviside step function, how does that affect the integral?

>>9728667
[math] P(X=x)=\sum_{y \in R_Y}P(X|Y=y) [/math]

Does there exist a non constant continuous function which maps R to to a compact set K?

>>9729066
What about tanh?

>>9729066
literally sinx maps R to [-1,1]

How reasonable would it be for me to go over a semester of calculus II material (integration techniques, volumes of revolution, L'Hopitals Rule, improper integrals, basic differential equations, series and sequences) in 2 days and get a 65% on the final exam? How many hours do I need to put in? My biggest weakness is sequences and series because I have not practiced them at all. My IQ is 120.

How reasonable would it be for me to go over a semester of calculus II material (integration techniques, volumes of revolution, L'Hopitals Rule, improper integrals, basic differential equations, series and sequences) in 2 days and get a 65% on the final exam? How many hours do I need to put in? My biggest weakness is sequences and series because I have not practiced them at all.

>>9729395
from the perspective of a 170 IQ student, you don't really need to study at all

You roll 3 dice. What is the probability of rolling at least 2 sixes?

Given
y = x^2
y =2x+3

How do you find both intersections mathematically?

I know I can find one:
x^2 -2x -3 = 0;
x^2-2x+1 - 4 = 0; (x-1)^2 = 4
x-1 = 2; x = 3
but how do I find -1?

>>9729449
>(x-1)^2 = 4
>x-1 = 2
Are you sure you are not forgetting something there?

>>9729461
?

>accidentally posted it in /mg/

It may be a very idiotic question but i don't want to pester my math teacher over it (too much).
Anyway, i just learned a bit about (not sure what the correct name is) "base change matrices" (you have two bases in vector spaces and this matrix allows you to go from one base [A] to another [B], plus it's inverse allows you to do the opposite (so from B to A))

What i wonder is: i know (well, more of a gut feeling) that this can be used to change the reference frame in physics but i don't exactly understand how and how it is adapted to cases where:
1) Relative position is constant
2) Relative position is not constant but relative velocities are, directions don't change too (example: two or more points moving away/toward each other at fixed velocities)
3) Relative accelerations change, directions don't change (for example someone looking at a falling object in absence of other forces [ie the object goes straight down])
4) Acceleration isn't constant in module and direction but it follows a known pattern (planetary motion and how it translates if you go from heliocentric to geocentric to jupitercentric etc)

Pic related for the 1st case, how do i make all my bases, matrices and transitions when analyzing the position of A from O1 and then O2? Assume that i use the unit vectors and the "direction" of the reference frame doesn't change (ie: i translate it from O1 to O2)

Please explain it like you would with a brainlet with down syndrome (cuz i'm one). I assume the base would look like {e1;e2;e3} where ei is the relevant column of the identity matrix nxn (in this case 3x3)

Also, all coordinates have been written with O1 as the origin point (mostly to not get bogged down with letters)

Thanks

>>9729463
>>>9729461 (You)
>?
(x-1)^2=4 already has two different solutions

>>9729468
yes I'm asking how would you o about finding it besides making mental assumption
what is the mathematical process

>>9729469
https://en.wikipedia.org/wiki/Quadratic_formula

>>9729469
>yes I'm asking how would you o about finding it besides making mental assumption
>what is the mathematical process
(x-1)^2=4 is solved both by x-1=2 and by x-1=-2....

>>9714575
this room is clean as fuck man, the desk is messy but they are working.

whats some basic chemistry equipment I should invest in if I'm getting into pyrotechnics?

>>9729542
Razor to shave head clean
Underwater glasses with extra-tick glass

>>9729542
Health insurance.

>>9729549
not sure what you mean by this lad
>>9729550
live in UK so it's free

>>9729449
Once you have found a root, divide the formula by (x - root):
x^2 -2x -3 / (x - 3) = x + 1

x + 1 = 0
That gives you the other root x = -1

>>9729571
how in the hell would I divide by x-3 anon

>>9729598
https://en.wikipedia.org/wiki/Polynomial_long_division

>>9729598
> how in the hell would I divide by x-3 anon
Dividing polynomials isn't much different to dividing integers. You're basically asking "what's the largest thing I can multiply the denominator by without exceeding the numerator, and what do I have to add to make up the difference".

For (x^2-2x-3)/(x-3), the numerator is quadratic, the denominator is linear, so the quotient can't be larger than linear. Both leading coefficients are 1, so the result looks like (x+k).

(x-3)(x+k) = x^2-3x+kx-3k = x^2+(k-3)x-3k.
k-3=-2 => k=1
(x-3)(x+1) = x^2-2x-3, i.e. there's no remainder (this is guaranteed because x-3 is known to be a factor, but in the general case polynomial division yields a quotient and a remainder).

>>9729542
ammonia and bleach are pretty much all you need for the rest of your life

>>9729770
I don't want to die though mate

>>9729774
we all do buddy

>>9729066
https://math.stackexchange.com/questions/676802/inverse-image-of-a-compact-set-is-compact

>>9729833
how can this be true? clearly sin : R -> [-1,1] is continuous and surjective?? and R is clearly not compact?

>>9729851
>clearly sin : R -> [-1,1] is continuous and surjective??
This is not a counterexample since R is not compact.

>>9729899
right, but this assumes X compact, not Y compact as the stupid questioner asked

>>9729449
Isn't this just babby's first factoring problem?
x^2-2x-3=(x-3)(x+1)

>>9730514
Now give a general algorithm for factoring arbitrary polynomials, retard