问题描述: 求和1xX+2xX^2+3xX^3+…+nxX^n. 1个回答 分类:数学 2014-10-19 问题解答: 我来补答 原式=SnX*Sn=1xX^2+2xX^3+…+nxX^(n+1)=Sn+1-(X+X^2+X^3+…+X^n+X^n+1)Sn+1-X*Sn=(X-X^n+2)/(1-X)Sn+1=Sn+(n+1)xX^n+1(1-X)Sn=(X-X^n+2)/(1-X)-(n+1)xX^n+1Sn=[X-(n+1)xX^n+1+nxX^n+2]/(1-X)^2 展开全文阅读