题目内容

在下面的横线里填上合适的数.
(1)
5
7
×
7
5
7
5
=1;
(2)9×
1
9
1
9
=1;
(3)
7
12
×
12
7
12
7
=1;
(4)
1
12
1
12
×12=1;
(5)
18
18
×
1
18
=1

(6)
19
17
19
17
×
17
19
=1

(7)
1
2
×
2
2
=
3
3
×
1
3
=
1
4
×
4
4
=
5
5
×
1
5
分析:根据倒数的意义,乘积是1的两个数互为倒数.由此解答即可.
解答:解:(1)
5
7
×
7
5
=1;
(2)9×
1
9
=1;
(3)
7
12
×
12
7
=1;
(4)
1
12
×12=1;
(5)18×
1
18
=1

(6)
19
17
×
17
19
=1

(7)
1
2
×2=3×
1
3
=
1
4
×4=5×
1
5

故答案为:
7
5
1
9
12
7
1
12
;18;
19
17
;2,3,4,5.
点评:此题考查的目的是理解倒数的意义和求法.
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