题干
观察下列各式： 1+
=2
2+
=3
3+
=4
a+
=8
a+b =____．
| 1 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 4 |
| 1 |
| 5 |
| 1 |
| 5 |
| 1 |
| b |
| 1 |
| b |
答案(点此获取答案解析）
4
