题目内容
观察下面算式,你发现了什么?
=
=1-
=
=
-
=
=
-
请你计算.
+
+
+
+
+
+
=
1 |
2 |
1 |
1×2 |
1 |
2 |
1 |
6 |
1 |
2×3 |
1 |
2 |
1 |
3 |
1 |
12 |
1 |
3×4 |
1 |
3 |
1 |
4 |
请你计算.
1 |
2 |
1 |
6 |
1 |
12 |
1 |
20 |
1 |
30 |
1 |
42 |
1 |
56 |
考点:分数的拆项
专题:计算问题(巧算速算)
分析:由
=
=1-
=
=
-
=
=
-
分子都是1,分母可以拆成连续两个自然数的积,这样的分数就等于以这两个自然数为分母,分子为1的两个分数的差,由此规律计算即可.
1 |
2 |
1 |
1×2 |
1 |
2 |
1 |
6 |
1 |
2×3 |
1 |
2 |
1 |
3 |
1 |
12 |
1 |
3×4 |
1 |
3 |
1 |
4 |
解答:
解:
+
+
+
+
+
+
=1-
+
-
+
-
+
-
+
-
+
-
+
-
=1-
=
.
1 |
2 |
1 |
6 |
1 |
12 |
1 |
20 |
1 |
30 |
1 |
42 |
1 |
56 |
=1-
1 |
2 |
1 |
2 |
1 |
3 |
1 |
3 |
1 |
4 |
1 |
4 |
1 |
5 |
1 |
5 |
1 |
6 |
1 |
6 |
1 |
7 |
1 |
7 |
1 |
8 |
=1-
1 |
8 |
=
7 |
8 |
点评:此题考查分数的拆分,注意分数分子分母的特点,找出规律解决问题.
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