题干
设Sn、Tn分别是等差数列{an}与{bn}的前n项和，若
=
，则
=____．
| S |
| n |
| T |
| n |
| n |
| 4 |
| 3 |
| n |
| + |
| 2 |
| a |
| 7 |
| b |
答案(点此获取答案解析）
| 9 |
It's yellow. It goes “ Quack …quack”