Question

Coefficient of x^n in the expression
(1-2x+3x^2-4x^3+...)^(-n) equals

Answer 1

1-2x+3x^2-4x^3+....=(1+x)^-2
=>(1-2x+3x^2-...)^-n=(1+x)^2n
thus coefficient of x^n is 2n^Cvn