问题
解答题
练习：求数列1，3+
|
答案
设数列1，3+
| 1 |
| 3 |
| 1 |
| 32 |
| 1 |
| 3n |
则Sn=1+3+32+…+3n+
| 1 |
| 3 |
| 1 |
| 32 |
| 1 |
| 3n |
=
| 3n+1-1 |
| 3-1 |
| ||||
1-
|
=
| 1 |
| 2 |
| 1 |
| 2 |
| 1 |
| 3n |
=
| 1 |
| 2 |
| 1 |
| 3n |
搜题请搜索小程序“爱下问搜题”
练习：求数列1，3+
|
设数列1，3+
| 1 |
| 3 |
| 1 |
| 32 |
| 1 |
| 3n |
则Sn=1+3+32+…+3n+
| 1 |
| 3 |
| 1 |
| 32 |
| 1 |
| 3n |
=
| 3n+1-1 |
| 3-1 |
| ||||
1-
|
=
| 1 |
| 2 |
| 1 |
| 2 |
| 1 |
| 3n |
=
| 1 |
| 2 |
| 1 |
| 3n |