若an=(2n-1)2的n次方 求sn
问题描述:
若an=(2n-1)2的n次方 求sn
答
sn=1*2^1+3*2^2+……+(2n-1)*2^n 2sn=1*2^2+3*2^3+……+(2n-1)*2^(n+1) 两式相减(即错位相减)得sn-2sn=1*2^1+2*2^2+2*2^3+……+2*2^n-(2n-1)*2^(n+1)-sn = -2+2*(2^1+2^2+2^3+……+2^n)-(2n-1)*2^(...