题干
约分：
=____，
=____．
| 4 |
| a |
| b |
| a |
| 3 |
| b |
| a |
| 2 |
| 2 |
| a |
| b |
| + |
| b |
| 2 |
| a |
| 2 |
| b |
| 2 |
