问题 解答题
用递等式计算.
7
12
×
8
21
×3
3
4
+
2
3
)÷
7
12
4
5
-
2
3
)÷
5
2
4
25
÷
25
12
8
9
×
9
7
÷
4
7
[
7
8
-(
1
2
+
1
4
)]÷
9
16
答案

(1)

7
12
×
8
21
×3

=

2
9
×3

=

2
3

(2)(

3
4
+
2
3
)÷
7
12

=

17
12
×
12
7

=

17
7

(3)(

4
5
-
2
3
)÷
5
2

=

2
15
÷
5
2

=

4
75

(4)2÷

4
25
÷
25
12

=2×

25
4
×
12
25

=2×(

25
4
×
12
25

=2×3

=6;

(5)

8
9
×
9
7
÷
4
7

=

8
7
÷
4
7

=2;

(6)[

7
8
-(
1
2
+
1
4
)]÷
9
16

=[

7
8
-
3
4
9
16

=

1
8
×
16
9

=

2
9

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