题目内容
数列{an}的前n项和公式是Sn,若an=
,则S8等于( )
1 |
n(n+2) |
A.
| B.
| C.
| D.
|
由题意可得an=
=
(
-
),
故S8=
[(1-
)+(
-
)+…+(
-
)+(
-
)]
=
(1+
-
-
)=
故选A
1 |
n(n+2) |
1 |
2 |
1 |
n |
1 |
n+2 |
故S8=
1 |
2 |
1 |
3 |
1 |
2 |
1 |
4 |
1 |
7 |
1 |
9 |
1 |
8 |
1 |
10 |
=
1 |
2 |
1 |
2 |
1 |
9 |
1 |
10 |
29 |
45 |
故选A
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