题干
一组按规律排列的式子：
，
，
，
，…则第n个式子是____ （n为正整数）．
| a |
| 2 |
| a |
| 3 |
| 4 |
| a |
| 5 |
| 6 |
| a |
| 7 |
| 8 |
答案(点此获取答案解析）
| a |
| 2 |
| n |
| - |
| 1 |
| 2 |
| n |
| a |
| 2 |
| a |
| 3 |
| 4 |
| a |
| 5 |
| 6 |
| a |
| 7 |
| 8 |
| a |
| 2 |
| n |
| - |
| 1 |
| 2 |
| n |
