Hello everyone, i'm studying for my exam. He gave us anice little pratice exam. Am i thinking too much about this one? Part (a) seems to easy. http://img235.imageshack.us/img235/1554/lastscan9dx.jpg [Broken] I think i'm trying to make x^(n-c) be x^(n) well to do this, i would add c to (n-c), but if u do this, you will have to subtract c from the indicies (the n under the sumation). So that would change, n = b, to n=b-c. Is that all i had to do here? Also in part b, i'm lost now! The directions say: show that a2 = 0, a3 = 0, and that the recurrance relation for this differential equation is: a_(n+4) = -a_n/((n+3)(n+4)) I've been using this as a referance to help me:http://tutorial.math.lamar.edu/AllBrowsers/3401/SeriesSolutions.asp [Broken] http://img126.imageshack.us/img126/2601/lastscan29ir.jpg [Broken] THanks!