# Search results

1. ### Conditional expectation

Question 1) I have X and Y independent stoch. variables What is E[X^2 * Y | X] ? does it generally hold that if X and Y are independent, then every function of X (eg X^2) is independent of Y? Does E[X^2 * Y | X] then become E[X^2|X]*E[Y|X] = E[X^2|X]*E[Y] since X^2 is independent of...
2. ### Multiple regression and Time Series

Hi, I'm in a college statistics course where I'm doing an assignement with Minitab. I have a one month time series of electricity use (hour intervals). I've attempted to remove the season effect from weekdays by index multiplication so all I'm left with (hopefully) is the effect from...
3. ### Mental math: Division of remainders

I'm working on moving away from long time slavery to the calculator Most forms of division and multiplication is going well now (long division and in some instances lattice multiplication) One thing I DON'T get though (and can't find any guides for) is dividing remainders. For example...
4. ### Cos(x): 8 in x's denominator

I have (from a complex equation problem) found the following angles in the answers: 5PI/8, 9PI/8, 13PI/8, 17PI/8 In the same assignement I found sin(PI/8) = .5*sqrt(2-sqrt(2)) and I found the cos(PI/8) value by using standard trig. identities. Is there an easy way to use this result to...
5. ### Riemann sums

Ok, so I have two questions regarding something I don't understand in my textbook (Adams) 1. 0 if 0<=x<1 or 1<x<=2 f(x) = 1 if x=1 (by "<=" i mean less than or equal) I'm supposed to show that it is Riemann integrable on that interval. They chose P to be: {0, 1-e/3...
6. ### Simple diff.eq

d/dx(y*x^2)=x^2/(1+x^2) I guess I can't write this as: dyx^2=x^2dx/(1+x^2) dy=dx/(1+x^2) beacuse I don't get the right answer... So what do I do?
7. ### Can someone show the steps?

how to go from: [(1+n)^n]/n to: (1+1/n)^n ?
8. ### Lagrange point

So im supposed to find the distance from the moon where the force on a particle from the earth and sun is equal. I get this expression (earth-moon distance is 400 000km): yMm/(r^2) = yMm / (400000km-r)^2 But from that I get r=200 000km and the answer should be 40 000km... whats wrong...
9. ### Can someone please explain the steps for me:

How can you go from: (1+x)^(k-1) / (1+x)^(2k) to: 1/ (1+x)^(k+1) ? Thanks!
10. ### Hints for integral

Ok so after a substituion I have this: (I dont know how to proceed) "integral of" (u-2) / sqrt(u^2 + 1) du and by the way, can someone tell me what cot^3(tan^-1(x)) equals? Thanks!
11. ### Problem with integral

Ok, so I have the integral of (x^2 + 1) / (x^3 + 8) dx I use partial fractions and end up with two integrals, the one I cannot solve is: 1/12 * "integral of" (7x-4) / [(x-1)^2 +3 ] dx With u=x-1 I get (7u-3) / (u^2+3) du But I have no Idea of how to solve it, the answer in the books...
12. ### Solve |x-1|e^x

Hi So Im a little confused about the absolute value sign here. Is the derivative right: [x-1/|x-1|]e^x + |x-1|e^x But what do I do when I set this to zero? Do I get two expressions, one for x>1 and one for x<1 ? (thus removing the absolute value signs)
13. ### Taylor Polynomial

Hi I have found the following TP (n=4) for g(x) = (1+5x)^1/5 P4(x) = 1+x-2x^2+6x^3-21x^4 Then they ask me to show that 0<E4(x)<80x^5 when x>0. I don't know how to start, or exactly what Im supposed to show...? I have found E4(x) to be( 399/[5(1+5X)^24/5] ) *x^5... And 0<X<x ...?
14. ### Proof by induction

Ok so I have found a formula for d^n/dx^n 1/x^2 = (-1)^n * (1+n)! * x^-(n+2) So I have to do d/dx [(-1)^n * (1+n)! * x^-(n+2)] and see what I end up with. But how do I do that. My book gives an example: (from d/dx (1+x)^-1) d/dx [(-1)^k * k!(1+x)^(-k-1)] = (-1)^k *...
15. ### Simple vector problems (hints please)

Hi, I'm stuck here: P1(1,2,3) and P2(2,2,2) Q1: Find a unitvector that points from P1 to P2. - A unitvector is a vector with length 1, right? But then what...? Q2: A point M lies on the center on the line from P1 to P2. What is the position vector to M? The sides of a parallellogram...
16. ### Epsilon-Delta proofs

Hi, right now Im struggeling with this (calc1). To be honest, I nearly don't understand a thing. What's going on, and when am I done with the proof? I can plug in the limits and the approached value into the formal definiton of a limit, but that's as far as I get. (I semi-get the easy ones...
17. ### Help with a limit

Hi, Lim(t->0) t / sqrt(4+t)-sqrt(4-t) I've stared at this for like half an hour :( Could someone please give me some hints of how I start factorizing this? Thanks.
18. ### Calculators Which calculator?

At the university I'm taking my physics bachelor, only these calculators are allowed on exams: Casio FX-82 Hewlett-Packard HP-30 Texas Instruments TI-30 So which could you reccomend? Btw, aren't these calculators somewhat "archaic"? Also, is it common not being allowed to use...
19. ### Your physics bachelor program

Hi, I'm curious about what your curriculum and book list look like. I've looked at the webpage of the university I'll begin at this fall, and was a bit perplexed to see that many courses are based on custom made issues (for courses like mechanics and such), not books. Also, in the 1. and...
20. ### Prospective salary

I'm just wondering... I'm going to start with an undergraduate in physics, from there I I'll pursue a graduate degree in something practical, something that's sought after in industry... But what? I know it's not healthy to pick a degree because of the income. But I don't want to work my...
21. ### Are graduate programs more competitive than

... undergraduate programmes? (I'm talking about admissions) I want to study abroad at a respected universe, but I don't have the grades to go directly to an undergraduate program. I'm taking my undergraduate degree in physics at a local university. The question is: how do I spend my three...
22. ### Calculus : A Complete Course (5th Edition)

Hi I've looked at the website of the university I have applied to, and they use these three books the first semesters. (physics bachelor degree) Calculus : A Complete Course (5th Edition) Robert A. Adams Linear Algebra and Its Applications David C. Lay Elementary Differential...
23. ### MBA programmes for engineers/scientists

I have applied to a physics bachelor degree. When I'm finnished with that I hope to have a chance applying to some schools in the USA (graduate program). But I'm also interested in economics, and I have heard that some schools offer students with background in physics and such specialized MBA...
24. ### Books like The Fabric of the Cosmos and

Books like "The Fabric of the Cosmos" and "Parallell Worlds" and "The Elegant Universe" Are there any new books out similair to these? I have finished all three of them, and have the taste for more. Please recommend some books, thanks!
25. ### A couple of questions

I have applied to a physics program (bachelor) at a university where i live. The program is "open", there are no grade limitations (it's the same most places in Norway - studying science is not that popular). But as far as I've understood, the university is good. They have exchange programs...
26. ### Two particles in a magnetic field

Illustration: http://home.no.net/erfr1/images/2.jpg "A particle, X with mass m and charge q starts with an inital velocity zero, and follows the red path indicated on the drawing. It follows a half circle when entering the magnetic field. A new particle, Y with mass m(same) and charge 2q...
27. ### Find the speed of the brick.

"A brick (M) is connected to another brick on a 30 degree slope. Don't mind the weight of the rope connecting these, and the friction. The mass of the right brick (M) is 3,5 kg What is the speed of the brick (M) when it have falled 0,5m?" I've drawed forces on the illustration. Here...
28. ### God and the uncertainty principle

First of all: I'm sorry if this question has been asked before. I tried a search, but couldn't find anything. So, the uncertainty principle prohibites anyone from knowing the exact location and velocity of a particle... If there was a God, wouldn't he/she have to know the exact location and...
29. ### Integration of (Cos X)^2

Hi, I just don't get this. I'm to lazy to type inn what I've done, so I just took a picture of my textbook: http://home.no.net/erfr1/images/1.jpg http://home.no.net/erfr1/images/2.jpg You're supposed to end up with the starting point, right? So you can divide the rest by two? Whatever I...
30. ### How far can the rocket go trough space?

Hi, I'm new to these boards. I hope I posted in the right category, (I believe collage is equivalent with gymnasium in Norway) Here's the problem: A rocket is fired of from the earth. The rocket's engine stops 85km above the earth's surface, then the rocket has a vertical velocity of...