Homework Statement
Calculate [x^n] (1-2x+x^2)^{(-k)} Homework Equations
Just the geometric series.The Attempt at a Solution
This is what I got so far [x^n] (1-2x+x^2)^{(-k)} = [x^n]((x-1)^2)^{(-k)} = [x^n] \frac{1}{(x-1)^{(2k)}}
Basically, how do I put this into a sum form? or can I just...