题目内容
观察下列各式:1 |
3 |
1 |
5 |
2 |
15 |
2 |
3×5 |
1 |
5 |
1 |
7 |
2 |
35 |
2 |
5×7 |
1 |
n |
1 |
n+2 |
2 |
n(n+2) |
1 |
1×3 |
1 |
3×5 |
1 |
5×7 |
1 |
n(n+2) |
分析:首先观察归纳得到规律为:
=
(
-
),然后利用规律求解即可求得答案.
1 |
n(n+2) |
1 |
2 |
1 |
n |
1 |
n+2 |
解答:解:
+
+
+…+
=
(1-
+
-
+
-
+…+
-
)=
(1-
)=
.
故答案为:
.
1 |
1×3 |
1 |
3×5 |
1 |
5×7 |
1 |
n(n+2) |
1 |
2 |
1 |
3 |
1 |
3 |
1 |
5 |
1 |
5 |
1 |
7 |
1 |
n |
1 |
n+2 |
1 |
2 |
1 |
n+2 |
n+1 |
2(n+2) |
故答案为:
n+1 |
2(n+2) |
点评:此题考查了分式的加减运算法.注意掌握规律
=
(
-
)是解此题的关键.
1 |
n(n+2) |
1 |
2 |
1 |
n |
1 |
n+2 |
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