问题 解答题
用简便方法计算.
5
12
+
7
15
+
8
15
+
7
12
=
1-
3
7
-
2
7
=
3
4
+
8
14
-
1
4
-
1
14
=
5
8
+
1
3
-
1
8
+
2
3
=
答案

5
12
+
7
15
+
8
15
+
7
12

=(

5
12
+
7
12
)+(
7
15
+
8
15
),

=1+1,

=2;

②1-

3
7
-
2
7

=1-(

3
7
+
2
7
),

=1-

5
7

=

2
7

3
4
+
8
14
-
1
4
-
1
14

=(

3
4
-
1
4
)+(
8
14
-
1
14
),

=

1
2
+
1
2

=1;

5
8
+
1
3
-
1
8
+
2
3

=(

5
8
-
1
8
)+(
1
3
+
2
3

=

1
2
+1,

=1

1
2

单项选择题
单项选择题