题干
先观察下列的计算，再完成习题：
| 1 |
| 2 |
| + |
| 1 |
| ( |
| 2 |
| − |
| 1 |
| ) |
| ( |
| 2 |
| + |
| 1 |
| ) |
| ( |
| 2 |
| − |
| 1 |
| ) |
| 1 |
| 3 |
| + |
| 2 |
| 3 |
| − |
| 2 |
| （ |
| 3 |
| + |
| 2 |
| ） |
| （ |
| 3 |
| − |
| 2 |
| ） |
| 1 |
| 4 |
| + |
| 3 |
| ( |
| 4 |
| − |
| 3 |
| ) |
| ( |
| 4 |
| + |
| 3 |
| ) |
| ( |
| 4 |
| − |
| 3 |
| ) |
请你直接写出下面的结果：
| 1 |
| 2 |
| + |
| 1 |
| ( |
| 2 |
| − |
| 1 |
| ) |
| ( |
| 2 |
| + |
| 1 |
| ) |
| ( |
| 2 |
| − |
| 1 |
| ) |
| 1 |
| 3 |
| + |
| 2 |
| 3 |
| − |
| 2 |
| （ |
| 3 |
| + |
| 2 |
| ） |
| （ |
| 3 |
| − |
| 2 |
| ） |
| 1 |
| 4 |
| + |
| 3 |
| ( |
| 4 |
| − |
| 3 |
| ) |
| ( |
| 4 |
| + |
| 3 |
| ) |
| ( |
| 4 |
| − |
| 3 |
| ) |
