## #math - Wed 18 Apr 2007 between 02:59 and 00:36

### NY Lost Funds

 TRWBW ?ConcernedWithSec: go with god ConcernedWithSec how old are you guys? thermoplyae 19 and getting older every second TRWBW PuppiesOnAcid: so if they are all 3 different points, and no 2 of them are verticle, than you can compute slope A to B and slope B to C, and they are on the same line if and only if those are equalPuppiesOnAcid: with me on the 2D case? PuppiesOnAcid Yep TRWBW PuppiesOnAcid: so now in 3D. well slope=rise/run. where run is change in x and rise is change in y, yes?PuppiesOnAcid: (that is in 2D that's what slope is) PuppiesOnAcid yes TRWBW PuppiesOnAcid: so in 3D you can think of two slopes, slope_y and slope_z. slope_y is (change in y)/(change in x) and slope_z=(change in z)/(change in x)PuppiesOnAcid: and the 3 points will be collinear if slope_y(A,B)=slope_y(A,C) *and* slope_z(A,B)=slope_z(A,C) PuppiesOnAcid Got it TRWBW PuppiesOnAcid: unfortunately, it gets more complicated if any of those (change in x)=0. that's like the verticle case in 2D, but in 3D its worse PuppiesOnAcid I am pretty sure that is not the case. TRWBW PuppiesOnAcid: then you are fine netpro25_ anyone know how to find the sum of the series? sum(n=0..oo, (1/(2^n)) TRWBW netpro25_: it's a geometric series, they should cover that in your booknetpro25_: i could give you the formula, or try to show you where it comes from netpro25_ k i am stuck on the algebralet me show you TRWBW ? netpro25_ i gave you the wrong problemhold onsum(n=0..oo, (1/(2^n) - (1/(3^n))i got the divided into two sums TRWBW ksame thing before, it's geometric sums netpro25_ do you plug in oo? TRWBW that means a sum of the form a_n=b*r^nyou got 1/2^n=1*(1/2)^n and 1/3^n=1*(1/3)^nbut in either case the formula is b/(1-r) netpro25_ ki see itah i seethanks trwbw you the man TRWBW np jadenbane What's a quick check to see if teo matricies are similar. detA=detB?Or do I have to find the eigenvalues of both? Kasadkad That's a necessary but not sufficient condition