| 1 |
| 1×4 |
| 1 |
| 4×7 |
| 1 |
| (3n-2)×(3n+1) |
则3Sn=
| 3 |
| 1×4 |
| 3 |
| 4×7 |
| 3 |
| (3n-2)×(3n+1) |
| 1 |
| 4 |
| 1 |
| 4 |
| 1 |
| 7 |
| 1 |
| (3n-2) |
| 1 |
| (3n+1) |
| 1 |
| (3n+1) |
| 3n |
| (3n+1) |
所以Sn=
| n |
| (3n+1) |
故答案为
| n |
| (3n+1) |
求和：1/1×4+1/4×7+…+1/(3n-2)×(3n+1)= _ ．
求和：
+
+…+
= ___ ．
| 1 |
| 1×4 |
| 1 |
| 4×7 |
| 1 |
| (3n-2)×(3n+1) |
数学人气：754 ℃时间：2020-02-04 09:39:17
优质解答
设Sn=
+
+…+
则3Sn=
+
+…+
=1-
+
-
+…+
-
=1-
=
所以Sn=
．
故答案为
则3Sn=
所以Sn=
故答案为
我来回答
类似推荐