求n乘二分之一的n次方的前n项和Sn,步骤谢谢!
发布网友
发布时间：2024-10-13 11:25
共1个回答
热心网友
时间：2024-10-19 23:58
(1/2)S= 1.(1/2)^2+2.(1/2)^3+...+n.(1/2)^(n+1) (2)
(1)-(2)
(1/2)S = [1/2^1+ 1/2^2+...+1/2^n ] - n.(1/2)^(n+1)
= ( 1- 1/2^n ) -n.(1/2)^(n+1)
= 1 - ((1/2)n+1).(1/2)^n
S =2 -(n+2).(1/2)^n
n乘二分之一的n次方的前n项和Sn
=S
= 2 -(n+2).(1/2)^n
热心网友
时间：2024-10-19 23:58
(1/2)S= 1.(1/2)^2+2.(1/2)^3+...+n.(1/2)^(n+1) (2)
(1)-(2)
(1/2)S = [1/2^1+ 1/2^2+...+1/2^n ] - n.(1/2)^(n+1)
= ( 1- 1/2^n ) -n.(1/2)^(n+1)
= 1 - ((1/2)n+1).(1/2)^n
S =2 -(n+2).(1/2)^n
n乘二分之一的n次方的前n项和Sn
=S
= 2 -(n+2).(1/2)^n
