Finding Value of C36-C37+C38 in f(x) McLaurin Series

[mit_hacker]

Homework Statement

Let f(x) = 1/(x^2+x+1).

Let f(x) = sum(from o to infinity) Cn x^n be the McLaurin Series representation for f(x). Find the value of C36-C37+C38.

Homework Equations

The Attempt at a Solution

I got the Taylor Series:

sum(from o to infinity) x^3n - sum(from o to infinity)x^(3n+1).

but have absolutely no idea what to do next. Please help!

 

[Avodyne]

What is C_n if n is a multiple of 3? If n is one more than a multiple of 3? If n is one less than a multiple of 3?