问题 解答题
用简便方法计算:
1
4
+(
2
3
+
3
4
1
4
+
1
3
+
1
4
+
2
3
5
9
-
4
5
-
1
5
9
7
+
1
8
+
3
8
+
5
7
答案

(1)

1
4
+(
2
3
+
3
4
),

=

1
4
+
3
4
+
2
3

=1+

2
3

=1

2
3

(2)

1
4
+
1
3
+
1
4
+
2
3

=(

1
4
+
1
4
)+(
1
3
+
2
3
),

=

1
2
+1,

=1

1
2

(3)

5
9
-
4
5
-
1
5

=

5
9
-(
4
5
+
1
5
),

=

5
9
-1,

=-

4
9

(4)

9
7
+
1
8
+
3
8
+
5
7

=

9
7
+
5
7
+(
1
8
+
3
8
),

=2+

1
2

=2

1
2

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