starting with geometric series sigma from n=0 to infinity of x^n find the sum of the series of sigma from n= 1 to infinity of n(x)^(n-1) lxl<1

b) find the sum of each of the following series,

1) sigma from n = 1 to infinity nX^n, lxl<1

2) sigma from n=1 to infity of n/2^n