题目内容
| 1 |
| 1×4 |
| 1 |
| 4×7 |
| 1 |
| 7×10 |
| 1 |
| (3n-2)(3n+1) |
A．
| B．
| C．
| D．
|
原式=
（1-
）+
（
-
）+…+
（
-
）=
[（1-
）+（
-
）+…+（
-
）]=
（1-
）=
；
故选A．
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 7 |
| 1 |
| 3 |
| 1 |
| 3n-2 |
| 1 |
| 3n+1 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 4 |
| 1 |
| 7 |
| 1 |
| 3n-2 |
| 1 |
| 3n+1 |
| 1 |
| 3 |
| 1 |
| 3n+1 |
| n |
| 3n+1 |
故选A．
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