题干
先化简，再求值： (a−3−
)÷
，其中a=﹣1．
| 7 |
| a |
| + |
| 3 |
| a |
| 4 |
| 2 |
| a |
| + |
| 6 |
| 7 |
| a |
| + |
| 3 |
| a |
| 4 |
| 2 |
| a |
| + |
| 6 |
• 
