题目内容
找规律
(1)
=1-
,
=
-
,
=
-
,…,
+
+
+
+
= (用简便方法做);
(2)1-
= ,
-
= ,
-
= ,1-
-
-
-
-
-
-
= .
(1)
1 |
2 |
1 |
2 |
1 |
6 |
1 |
2 |
1 |
3 |
1 |
12 |
1 |
3 |
1 |
4 |
1 |
2 |
1 |
6 |
1 |
12 |
1 |
20 |
1 |
30 |
(2)1-
1 |
2 |
1 |
2 |
1 |
4 |
1 |
4 |
1 |
8 |
1 |
2 |
1 |
4 |
1 |
8 |
1 |
16 |
1 |
32 |
1 |
64 |
1 |
128 |
考点:分数的巧算
专题:计算问题(巧算速算)
分析:(1)通过观察,每个分数都可以拆成两个分数相减的形式,然后通过加减相互抵消,求得结果.
(2)通过观察发现:后一个数的分母是前一个数分母的2倍,相减得出结果为后一个数,据此解答.
(2)通过观察发现:后一个数的分母是前一个数分母的2倍,相减得出结果为后一个数,据此解答.
解答:
解:(1)
+
+
+
+
=1-
+
-
+
-
+
-
+
-
=1-
=
(2)1-
=
,
-
=
,
-
=
1-
-
-
-
-
-
-
=
故答案为:
,
,
,
,
.
1 |
2 |
1 |
6 |
1 |
12 |
1 |
20 |
1 |
30 |
=1-
1 |
2 |
1 |
2 |
1 |
3 |
1 |
3 |
1 |
4 |
1 |
4 |
1 |
5 |
1 |
5 |
1 |
6 |
=1-
1 |
6 |
=
5 |
6 |
(2)1-
1 |
2 |
1 |
2 |
1 |
2 |
1 |
4 |
1 |
4 |
1 |
4 |
1 |
8 |
1 |
8 |
1-
1 |
2 |
1 |
4 |
1 |
8 |
1 |
16 |
1 |
32 |
1 |
64 |
1 |
128 |
1 |
128 |
故答案为:
5 |
6 |
1 |
2 |
1 |
4 |
1 |
8 |
1 |
128 |
点评:仔细观察,根据规律进行解答.
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