问题
解答题
练习：求数列
|
答案
令S=
| 2 |
| 2 |
| 4 |
| 22 |
| 6 |
| 23 |
| 2n |
| 2n |
则
| 1 |
| 2 |
| 2 |
| 22 |
| 4 |
| 23 |
| 2n-2 |
| 2n |
| 2n |
| 2n+1 |
两式相减可得，
| 1 |
| 2 |
| 1 |
| 22 |
| 1 |
| 23 |
| 1 |
| 2n |
| 2n |
| 2n+1 |
| ||||
1-
|
| n |
| 2n |
| 1 |
| 2n-1 |
| n |
| 2n |
∴s=4-
| 2+n |
| 2n-1 |
搜题请搜索小程序“爱下问搜题”
练习：求数列
|
令S=
| 2 |
| 2 |
| 4 |
| 22 |
| 6 |
| 23 |
| 2n |
| 2n |
则
| 1 |
| 2 |
| 2 |
| 22 |
| 4 |
| 23 |
| 2n-2 |
| 2n |
| 2n |
| 2n+1 |
两式相减可得，
| 1 |
| 2 |
| 1 |
| 22 |
| 1 |
| 23 |
| 1 |
| 2n |
| 2n |
| 2n+1 |
| ||||
1-
|
| n |
| 2n |
| 1 |
| 2n-1 |
| n |
| 2n |
∴s=4-
| 2+n |
| 2n-1 |