Question: generalized geometric series

I want to prove by Maple if  -1<x<1 and n is positive integer then

sum(k^n*x^k, k = 1 .. infinity) = (sum([sum((-1)^(m+1)*(binomial(n+1, m-1))(r-m+1)^n, m = 1 .. r)]*x^r, r = 1 .. n))/(1-x)^(n+1)

I would appreciate for any help.

                                                            Sandor

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