Question

常数项级数求和

Answer 1

就这个还叫简答题,什么老师?

注意到

(n+1)² = (n+1)+(n+1)n,

作幂级数

f(x) =∑(n≥0)(n+1)x^n,g(x) = ∑(n≥1)(n+1)nx^(n-1),|x|