Apr 15, 2012 #1 Poirot1 Messages 243 Reaction score 0 Find the sum to infinity of the series $1 +2z +3z^2+4z^3+...$
Apr 15, 2012 #2 Opalg Gold Member MHB Messages 2,778 Reaction score 13 Integrate it, find the sum of the integrated series, then differentiate it.