Math thread! Come in and have some pi...

[ctownballer04]

Missed this post yesterday. Oops, I didn't really mean to say that E[X] = E[Y] = E[X|X+Y=10]. Conditional expectation is definitely it's own thing and is used a lot in stuff like time series analysis. But I can see how you would think I meant that considering it's what I quoted and also I used that in the last line of my attempt at a solution -- again oops. What I'm unsure of is being able to substitute directly like that and get rid of the conditioning and have it still be equal.

If the substitution I did is legit, you can just plug lambda back into 4lambda - 10 or 10 - 2lambda instead of the original equation like I did on the last line.

I've been thinking about going over my stats/probability book again, and I think this problem might have convinced me it would be a good thing to do.

I'm reminded of a quote from machine learning expert Michael Jordan after giving a book list: textbooks should be read three times, "the first time you barely understand, the second time you start to get it, and the third time it all seems obvious"

I think I actually know how to do this now, will bump in a few.

The method I'm using is way more complicated but from the looks of it (not finished quite yet), the answer might result in the same thing you posted but through much more work. I'll post back in the next hour or so, still working on it.

[PTaash]

Hey there, hoping to get some assistance with a little problem I had.

I have to find the inverse of (y = x+3/x) algebraically, and I can't seem to wrap my head around it.

I get stuck at xy = y+3, can anyone help me finish it off?

I feel so stupid but I just can't figure it out,
Many thanks!

[apsizzle2]

A weather rocket is launched straight up. The rocket motor provides constant acceleration for 16 seconds, then the motor stops. The altitude of the rocket is 5100m 20 seconds after launch.

What was the rockets acceleration for the first 16 seconds? What was the rockets speed at 5100m?

In need of desperate homework help!

[ctownballer04]

Hey there, hoping to get some assistance with a little problem I had.

I have to find the inverse of (y = x+3/x) algebraically, and I can't seem to wrap my head around it.

I get stuck at xy = y+3, can anyone help me finish it off?

I feel so stupid but I just can't figure it out,
Many thanks!

No problem man.

y=(x+3)/x
We want to solve for x.
Your first step was good
yx=(x+3)
subtract x which yields:
yx-x=3
factor the left hand side, which yields
x*(y-1)=3 <-- If this step is what threw you off, just play around with the left hand side, notice that x*(y-1)=xy-x, they are the same thing.
x=3/(y-1)
switch your x's and y's
y=3/(x-1) <-- this is your inverse function.

Use parentheses. I think you mean: (x+3)/x.

At the point of xy=y+3, subtract y from both sides.

xy-y=3

factor out y.

y(x-1)=3

finally divide both sides by (x-1)

Thunder=stolen.

[PrimeraRS]

A weather rocket is launched straight up. The rocket motor provides constant acceleration for 16 seconds, then the motor stops. The altitude of the rocket is 5100m 20 seconds after launch.

What was the rockets acceleration for the first 16 seconds? What was the rockets speed at 5100m?

In need of desperate homework help!

You should have physics formula sheet no?

are we assuming gravity is constant or there is none? And is v0y= 0?

edit:typo

[PTaash]

No problem man.

y=(x+3)/x
We want to solve for x.
Your first step was good
yx=(x+3)
subtract x which yields:
yx-x=3
factor the left hand side, which yields
x*(y-1)=3 <-- If this step is what threw you off, just play around with the left hand side, notice that x*(y-1)=xy-x, they are the same thing.
x=3/(y-1)
switch your x's and y's
y=3/(x-1) <-- this is your inverse function.




Thunder=stolen.

Many thanks to you and MiscMathematician!

Hopefully I do well on the exam tomorrow!

Thanks once again, Ill be back again, I'm sure of it.

[ctownballer04]

Missed this post yesterday. Oops, I didn't really mean to say that E[X] = E[Y] = E[X|X+Y=10]. Conditional expectation is definitely it's own thing and is used a lot in stuff like time series analysis. But I can see how you would think I meant that considering it's what I quoted and also I used that in the last line of my attempt at a solution -- again oops. What I'm unsure of is being able to substitute directly like that and get rid of the conditioning and have it still be equal.

If the substitution I did is legit, you can just plug lambda back into 4lambda - 10 or 10 - 2lambda instead of the original equation like I did on the last line.

I've been thinking about going over my stats/probability book again, and I think this problem might have convinced me it would be a good thing to do.

I'm reminded of a quote from machine learning expert Michael Jordan after giving a book list: textbooks should be read three times, "the first time you barely understand, the second time you start to get it, and the third time it all seems obvious"



Slacker and MiscMathematician, I think you guys have mentioned that you've taught classes before. I'm curious what you did to prepare. I've been thinking of maybe getting a job as a tutor, but I'm scared to death of saying idiotic stuff and giving people wrong answers.

YOU WERE RIGHT ALL ALONG!!!!! I figured out how to do it in a worse way but it results in an answer of 10/3, i'll supply my work on here in a minute. I'm going to copy down your answer onto the paper I bring in tomorrow as I imagine that is what he wanted all along(considering my way is in my opinion far too dificult for him to test on in a 50 minute exam based on where we are in the class) and I'm also going to turn in my answer to show him that I seriously spent some time and tried to do it even though I thought it was harder than it really was.

[apsizzle2]

Gravity constant.. And
I was unsure on v0 = 0 also.. This
Is why
I couldn't figure it out

[ctownballer04]

Missed this post yesterday. Oops, I didn't really mean to say that E[X] = E[Y] = E[X|X+Y=10]. Conditional expectation is definitely it's own thing and is used a lot in stuff like time series analysis. But I can see how you would think I meant that considering it's what I quoted and also I used that in the last line of my attempt at a solution -- again oops. What I'm unsure of is being able to substitute directly like that and get rid of the conditioning and have it still be equal.

If the substitution I did is legit, you can just plug lambda back into 4lambda - 10 or 10 - 2lambda instead of the original equation like I did on the last line.

I've been thinking about going over my stats/probability book again, and I think this problem might have convinced me it would be a good thing to do.

I'm reminded of a quote from machine learning expert Michael Jordan after giving a book list: textbooks should be read three times, "the first time you barely understand, the second time you start to get it, and the third time it all seems obvious"



Slacker and MiscMathematician, I think you guys have mentioned that you've taught classes before. I'm curious what you did to prepare. I've been thinking of maybe getting a job as a tutor, but I'm scared to death of saying idiotic stuff and giving people wrong answers.

Sorry for poverty picture. It relies from the fact that the sum of two independent poisson RVs is itself a poisson RV (I knew this), and that a poisson conditioned on a poisson is a binomial (I didn't know this). Ie: P[X|X+Y=10] is a binomial RV.

[ChrisVigor]

Concerning vectors in a acceleration graph, how does a vector in quadrant 3 have a bigger x component than a vector in quadrant 1? Or does each quadrant just signify a different direction? My mind starts to grasp the concept but then add kicks in.

My book says everything on top of the x axis is positive (regardless of slope) and everything below is negative (again regardless if its a positive or negative slope). Does it mean direction? Book fukin suks m8

[bogui94]

try to give your thoughts if you get stuck and i or someone else will help if we can.

 
-3/8 x^3 + 13/8 x^2 - 1/4 x + 1
 Stuck on a) 

Polynomials for c)

	
	
1, 2, 
2x^2 + 2, 2x^2 + 2x + 2, 2x^2 +2x + 2, 2x^2 + x, 2x^2 + x +1, 2x^2 + x + 2, x^2 + 2x, x^2 + 2x+ 2, x^2 + x, x^2 + x + 2, x^2 + x + 1
 Which one's am I missing?
 71
 s = 3
 a)
(r-b)/(p-1) = k
r = k(p-1)+ b
a^(p-1) = 1 mod p
a^r = a^(k(p-1)+b) 
      = a^(k(p-1)) * a^b 
      = 1^k * b 
      = a^b mod p
a^b  = a^b

b)
Direct Proof:
x = g(f(x))
g(x) = x^(d) mod p
f(x) = x^(e) mod p
de = 1 mod (p-1)
ed = (k(p-1)+1) mod p   *lemma
x = (x^(e) mod p)^(d) mod p
  = x ^ (ed) mod p
  = x ^(k(p-1)+1) mod p
  = x ^(k(p-1)) * x mod p
x = x mod p 
c)
Yes.

Here you go, brah:

http://www.mathcelebrity.com/chinese...ainder+Theorem


Obviously, -34 isn't the answer you're looking for since it's negative, so just add 7*5*3 = 105 to -34 to get the smallest positive solution.

So x = -34 + 105 = 71

Note that it satisfies all 3 equations.

tyvm.

[Slacker23]

2. Stuck on a)

Simplest way to do a):

You know that, in $F_p$, you have that $x^p=x$ for any $x$ so, given a polynomial $\sum a_nx^n$ you can re-write each term as follows:
$$a_{kp+r}x^{kp+r}=a_{kp+r}(x^p)^kx^r=a_{kp+r}x^kx ^r=a_{kp+r}x^{k+r}$$

Iterate this enough times and it will eventually re-write all of your terms as being powers smaller than or equal to $p-1$.

Incidentally, I'm using "=" abusively in the above. Those polynomials are equivalent over $F_p$ but not equal, which will become important when you see $F_{p^n}$... but there's no point bothering with that for now.

[NephilimRising]

Need help with this problem

The force acting on a moving charged particle in a magnetic field B is F=q(vXB) where q is the electric charge of the particle and v is the velocity. Suppose that a particle moves in the xy-plane with a uniform B in the z-direction. Assuming Newton's 2nd law m(dv/dt)=F, show that

a) force and velocity are perpendicular

b) that force and magnitude have constant velocity

HINT: find (d/dt) (vdotv)

Our teacher said we have to do this with index notation and that two identities we will find useful are (we also have to prove these with index notation)

A dot (AcrossB)=0

and

(AcrossB) dot (AcrossB) = something (we have to derive this, he didn't tell us what it was)


I've proved the identities he's asked us to prove and I believe I've done part A right, it's part B that I need help on (proving the magnitudes of F and v are constant)

Here's my attached work for the identities and part A)

As always, any help is appreciated

[NeedPhysicsHelp]

Please help me finish this problem. Also I think I literally got the third question in the first part right by fluke. I subtrcated 1276 - 481 and got 795 J and it accepted the answer, correcting it to be 801.5 J though. So I need an explanation of how that is supposed to be done too lol.

[NephilimRising]

NVM figured it out. I think. Answer incoming.

Edit: CTownBaller is a math god now. I remember when we were both taking diff eq. Jelly.

[ctownballer04]

I have my second Discrete exam in the morning and I'm working on this exam review my prof posted and I can't come up w/ an example that makes this T and I know it has to be really easy but I'm just not seeing it.

"If R and S are relations on AxA and R and S are both anti-symmetric, RUS is anti-symmetric"
This appears to me that its true because I can't think of a counter example, but my prof has this as false, can anyone throw a quick counter example at me so I can sleep tonight lol.

If R and S are anti-symmetric they have to just be sets of order pairs {x,x} where x=x for all x in A. So I don't so how combining a bunch of these pairs into a single set could result in an set that doesn't pass for anti-symmetry.

Thanks

NVM figured it out. I think. Answer incoming.

Edit: CTownBaller is a math god now. I remember when we were both taking diff eq. Jelly.

not even close brah... i'm still a plebeian.

Is this multivariable calc or a physics class of some sort?

[NeedPhysicsHelp]

Does anyone know a site I can post physics questions too ?

I'm willing to pay monthly for it.

Would chegg work?

[ctownballer04]

antisymmetric means it cannot contain both (a,b) and (b,a). or, if it did and it is assumed antisymmetric, you must have a=b.

Take R to be the less-than relation, S to be the greater than relation. Then (1,2) and (2,1) belong to RuS




possibly chegg. or physicsforums or yahoo answers even. if you dont mind typing up the questions and posting your work physics stack exchange might be good

thanks as always.

[NephilimRising]

I have my second Discrete exam in the morning and I'm working on this exam review my prof posted and I can't come up w/ an example that makes this T and I know it has to be really easy but I'm just not seeing it.

"If R and S are relations on AxA and R and S are both anti-symmetric, RUS is anti-symmetric"
This appears to me that its true because I can't think of a counter example, but my prof has this as false, can anyone throw a quick counter example at me so I can sleep tonight lol.

If R and S are anti-symmetric they have to just be sets of order pairs {x,x} where x=x for all x in A. So I don't so how combining a bunch of these pairs into a single set could result in an set that doesn't pass for anti-symmetry.

Thanks



not even close brah... i'm still a plebeian.

Is this multivariable calc or a physics class of some sort?

"Theoretical Physics"...........basically a math class covering miscellaneous topics not covered in calc 1-3, linear algebra, and diff eq.

How are you enjoying upper level math?

Chit looks pretty hardcore.

[ctownballer04]

"Theoretical Physics"...........basically a math class covering miscellaneous topics not covered in calc 1-3, linear algebra, and diff eq.

How are you enjoying upper level math?

Chit looks pretty hardcore.

Discrete Math is pretty easy, we covered a lot of stuff I covered in Group Theory last term but it's less difficult, I got a 98% on the midterm so I've just been coasting and now I'm hoping I don't fuk up my 2nd exam tomorrow. I feel good enough though.

Taking Applied Probability which I found very difficult but I have a horrendous professor for this one. I really like the content though but I feel its graded rather unfairly and it's just a poorly ran class (we have 2 midterms and a final in this class encompassing 80% of our grade, those two midterms both had 3 questions on them so you miss a single question and that's like a few percent of your entire class grade. Our midterm was last week and one of the 3 problems not a single person in the class got right and then he sent us an e-mail how disappointed he was in us and all this bullchit. Also. I'm one of like 5 undergrads with the other 10 or 11 people being grad students. Normally when classes are split like this (in my experience), the grad students might have a slightly different exam or an extra hw problem or something but its all the exact same in this class and there is no curve. So my conclusion is that I really like the material but the entire situation is just terrible and I won't be taking the 2 part in the sequence (partially because I physically can't due to another class constraint but mainly the professor, he'll be the first professor I write a negative review for in 5 years of college).

Then I have i'm taking the second course in a sequence on mathematical game theory. It's pretty cool, I enjoy it. It's really applicable to life in a general sense but the work we do in the class is way more advanced than anything I feel I'd ever use in real life. Brb building this ridiculously long model to determine where the value of coalition formation comes from and under which stochastic vector most fairly assigns this value to the members. This class I learn a lot about problem solving and critical thinking which in my opinion is one of the most important things to take away from school because there is plenty of other just definitions and stuff I'll memorize for school and then just not remember anything about the subject a year or two later.

Sorry for such the long post, moral of the story I like it but it's obviously a lot of work because I'm taking finance and economics classes on top 3 math classes so I'm kinda dying. Next term will be nice though, I'm taking Ring and Field Theory and that is it for math, the rest will be finance and business capstone.


What's up with you? Are you still doing a math major?

[SCAR-H]

Discrete Math is pretty easy, we covered a lot of stuff I covered in Group Theory...

Fuark. I'm currently taking discrete math and I think I have it easy. My professor is incorporating tonnes programming into our assignments and we can write our midterms in any language we want.

ex instead of writing (PvQ) -> R we can write P + Q <= R which makes it a whole lot easier with boolean expressions imo
There are some people in the class who have absolutely no clue how to program, and I get the feeling it will be their most difficult class this semester.

Current assignment has us generating truth tables from reverse polish notation input, which is something anyone can do by hand but becomes a bit complicated when you implement it in code.

ex:

[NeedPhysicsHelp]

antisymmetric means it cannot contain both (a,b) and (b,a). or, if it did and it is assumed antisymmetric, you must have a=b.

Take R to be the less-than relation, S to be the greater than relation. Then (1,2) and (2,1) belong to RuS




possibly chegg. or physicsforums or yahoo answers even. if you dont mind typing up the questions and posting your work physics stack exchange might be good

Chegg would probably be the only viable one I think, since the others would take forever to get back to you.

Can you list the physics topics that I can actually ask you?

http://labman.phys.utk.edu/phys135/Modules.htm

edit: I was just in class and borrowing someones chegg, literally most questions don't even get answered, lol. Same with the other places. I guess the only way would be to pay some tutor to do it or something, but that would be really expensive. damn

[ctownballer04]

mostly just projectile motion, some force and gravity questions, maybe circuitry.

but youd be surprised about yahoo answers. people love their fukking points on there and being all-stars or whatever gold status means. id literally need to refresh, click a question 10 seconds old, and answer as fast as possible to be first lol. in the math section anyway

I can confirm loll.

I remember like one of my first terms at CC I took an online econ class before I knew anything about econ. I had a 100 question take home final that I had a week to do. I made like 25 yahoo answers accounts and just posted nearly ever question. What a good student I was.

[ctownballer04]

Fuark. I'm currently taking discrete math and I think I have it easy. My professor is incorporating tonnes programming into our assignments and we can write our midterms in any language we want.

ex instead of writing (PvQ) -> R we can write P + Q <= R which makes it a whole lot easier with boolean expressions imo
There are some people in the class who have absolutely no clue how to program, and I get the feeling it will be their most difficult class this semester.

Current assignment has us generating truth tables from reverse polish notation input, which is something anyone can do by hand but becomes a bit complicated when you implement it in code.

ex:

Is this in a math department or a discrete structures course in a CS department?

We have no coding in mine. We've covered: truth tables, proofs, combinatorics, equivalence relations, partial orders, and a few other applied things. I had never done truth tables before this class formally but I read about them in my intro to proof writing book I used a bit before Group Theory and then I've already done all the proof types and equivalence relations in group theory, combinatorics in probability classes. The only things I had never really seen were partial orders.

[SCAR-H]

Is this in a math department or a discrete structures course in a CS department?

We have no coding in mine. We've covered: truth tables, proofs, combinatorics, equivalence relations, partial orders, and a few other applied things. I had never done truth tables before this class formally but I read about them in my intro to proof writing book I used a bit before Group Theory and then I've already done all the proof types and equivalence relations in group theory, combinatorics in probability classes. The only things I had never really seen were partial orders.

It falls under both.

Look up logic gates if you want to see more boolean expression truth tables.

[ctownballer04]

It falls under both.

Look up logic gates if you want to see more boolean expression truth tables.

We covered this stuff but blew through it cause its much more emphasized in our discrete structures class in the CS department.

[NeedPhysicsHelp]

Can anyone here do impulse-momentum theorem problems like this one or no?

[tk217]

Why is 1+2+3+4+5+6 +........ = -1/12?

[tk217]

it is what it should be if it converged in the normal sense, but it does not. different values can come from this as well, if you change the definition of convergence

see this math.se post http://math.stackexchange.com/questi...-cdots-frac112

So I suppose ... the question should be to a mathematical philosopher is... why is it ... an acceptable answer.

Also there are way to many math jokes on that thread.

[NephilimRising]

Discrete Math is pretty easy, we covered a lot of stuff I covered in Group Theory last term but it's less difficult, I got a 98% on the midterm so I've just been coasting and now I'm hoping I don't fuk up my 2nd exam tomorrow. I feel good enough though.

Taking Applied Probability which I found very difficult but I have a horrendous professor for this one. I really like the content though but I feel its graded rather unfairly and it's just a poorly ran class (we have 2 midterms and a final in this class encompassing 80% of our grade, those two midterms both had 3 questions on them so you miss a single question and that's like a few percent of your entire class grade. Our midterm was last week and one of the 3 problems not a single person in the class got right and then he sent us an e-mail how disappointed he was in us and all this bullchit. Also. I'm one of like 5 undergrads with the other 10 or 11 people being grad students. Normally when classes are split like this (in my experience), the grad students might have a slightly different exam or an extra hw problem or something but its all the exact same in this class and there is no curve. So my conclusion is that I really like the material but the entire situation is just terrible and I won't be taking the 2 part in the sequence (partially because I physically can't due to another class constraint but mainly the professor, he'll be the first professor I write a negative review for in 5 years of college).

Then I have i'm taking the second course in a sequence on mathematical game theory. It's pretty cool, I enjoy it. It's really applicable to life in a general sense but the work we do in the class is way more advanced than anything I feel I'd ever use in real life. Brb building this ridiculously long model to determine where the value of coalition formation comes from and under which stochastic vector most fairly assigns this value to the members. This class I learn a lot about problem solving and critical thinking which in my opinion is one of the most important things to take away from school because there is plenty of other just definitions and stuff I'll memorize for school and then just not remember anything about the subject a year or two later.

Sorry for such the long post, moral of the story I like it but it's obviously a lot of work because I'm taking finance and economics classes on top 3 math classes so I'm kinda dying. Next term will be nice though, I'm taking Ring and Field Theory and that is it for math, the rest will be finance and business capstone.


What's up with you? Are you still doing a math major?

Physics Major, and don't worry about the long post. I enjoyed it. I've been on viibryd (an anxiety med) for a few months and I've been more relaxed. I haven't succumbed to anxiety just yet and I've been doing well in my classes.

Although I should probably wait until I've completed the semester to talk about the new philosophy I'm trying to implement....I'm gonna talk about it anyway. I used to be so worried about being "perfect" that I would get mad at teachers for not doing everything "my way", and it would hold me back a lot because I kept dropping classes. In a sense I was "running away".

Now I realize I don't have to be perfect, I just have to be good and do the best I can under the circumstances. Even If I can't be perfect, it's worth doing it anyway. I'm not trying to avoid strife anymore, I'm trying to imbue that strife with meaning and use it as a tool for self-improvement.

So you should think about taking that 2nd class anyway despite having that douchey teacher. Unless it would seriously fuk your GPA of course.