题干
化简求值，
−
⋅
，其中x=2．
| 3 |
| x |
| x |
| 1 |
| x |
| x |
| + |
| 1 |
| x |
| 2 |
| 1 |
| x |
| 3 |
| x |
| x |
| 1 |
| x |
| x |
| + |
| 1 |
| x |
| 2 |
| 1 |
| x |
