# Recent content by imsleepy

1. ### Eigenval/vect question, double check my answers, dont make sense

A times (-1,-1,1) i (incorrectly) did: 1x-1 + 0x-1 + 2x-1 0x-1 + 1x-1 + 2x-1 2x 1 + 2x 1 + 3x 1 giving -1-2 -1-2 2+2+3 resulting in (-3,-3,7) which is incorrect. i know how to do it now, thanks ehild and lanedance. shouldve remembered this from years ago...
2. ### Eigenval/vect question, double check my answers, dont make sense

ok i was multiplying column of matrix by each row of the vector, when i should be multiplying the rows of the matrix by the vector and adding terms. my bad.
3. ### Eigenval/vect question, double check my answers, dont make sense

ok yeah my bad, the evect for lambda = -1 is (-1,-1,1) (i rushed). but multiplying A with (-1,-1,1) gives (-3,-3,7), which still doesnt make sense >:/
4. ### Eigenval/vect question, double check my answers, dont make sense

eigenval/vect question, double check my answers, dont make sense............. Homework Statement find eigenvalues and eigenvectors of matrix A = 102 012 223 Homework Equations A -λI etc blah The Attempt at a Solution I'm getting λ = 1, -1, 5. For λ = 1, v = (-1,1,0)t (t...
5. ### PDE questions

from there onwards, i simply cannot understand what worked solutions are doing >_<
6. ### PDE questions

du/dx (0,y) = 0 so, gradient at 0,y is equal to 0? would this be just the y-axis (up to point H) that is insulated?
7. ### PDE questions

ok found some stuff in my notes. i think the du/dx (0,y) = 0 line tells you that something is insulated. i've done some question in my book (obviously lecturer has done it and i was merely copying it, lol), and i have written down: uxx + uyy = 0 u(0,y) = 0 u(a,y) = 0 u(x,0) = x (maintain...
8. ### PDE questions

ehh my head's not working, i should go to bed soon. question 4. no clue. H and L are just arbitrary points on the y and x axis respectively, i presume.. what do each of those initial constraints mean, please? and how do i know what is insulated?
9. ### PDE questions

ughh i really have no idea what to do now. also i've wasted too much time on one question. gonna try to do the PDE one. you said i'll give this a shot and post up working out as i go.
10. ### Quadric surface question, given 3x3 matrix A and (x^T)Ax=6

awesome, thank you :)
11. ### Quadric surface question, given 3x3 matrix A and (x^T)Ax=6

this is my working out: http://i.imgur.com/1hsQS.jpg i sort of figured out how to do this a few mins ago lol. it doesnt seem too hard. it's sort of like... multiplying the first number in the matrix A by it's position in the matrix (x1 * x1) which is basically the coordinates of the value...
12. ### PDE questions

im not used to tex but i'll keep that in mind. yes my f is in that form. so i have a_0 = \frac{1}{2} b_n = \frac{1-(-1)^{n}}{n*Pi} would i just let c_0 and d_n equal a_0 and b_n respectively?
13. ### PDE questions

http://i.imgur.com/0MiDc.jpg my result as a sum of infinite series at the top, the rest is getting the first 4 non-zero terms. and im not following you from your second sentence onwards...
14. ### PDE questions

firstly is f(x) = 2 + (2/Pi)*sin(x) + (2/Pi)*sin(3x) correct? then i'd use k = 2/pi, and theta would be 1 and 3?
15. ### PDE questions

yeah that too! ok particular solution, this one i'd have to guess depending on what f(x) is (which i've never learnt how to do lol). method of undetermined coefficients, i think it is. my guess, something related to a trig function because we have a couple of sine's in f(x)? so according to...