{an}中,an=(2n-1)+1/2^n,求Sn
问题描述：
{an}中,an=(2n-1)+1/2^n,求Sn
答
解:Sn=a1+a2+a3+...+an=[1+(1/2)^1]+[3+(1/2)^2]+[5+(1/2)^3]+...+[(2n-1)+(1/2)^n]=[1+3+5+...+(2n-1)]+[(1/2)^1 + (1/2)^2 + (1/2)^3+...+(1/2)^n]={n[1+(2n-1)]/2}+{(1/2)[1-(1/2)^n]/(1-1/2)}=n^2+[1-(1/2)^n]=n...