题目内容
计算下面各题,怎样计算简便就怎样计算.
2
-(
+
)
+
+
-
+
.
2
2 |
9 |
2 |
9 |
5 |
12 |
1 |
5 |
3 |
8 |
4 |
5 |
8 |
9 |
2 |
3 |
1 |
3 |
分析:(2)可以运用减去两个数的和等于分别减这两个数来简算;
(2)运用加法交换律简算;
(3)运用加法结合律简算.
(2)运用加法交换律简算;
(3)运用加法结合律简算.
解答:解:(1)2
-(
+
),
=2
-
-
,
=2-
,
=1
;
(2)
+
+
,
=(
+
)+
,
=1+
,
=1
;
(3)
-
+
,
=
-(
-
),
=
-
,
=
.
2 |
9 |
2 |
9 |
5 |
12 |
=2
2 |
9 |
2 |
9 |
5 |
12 |
=2-
5 |
12 |
=1
7 |
12 |
(2)
1 |
5 |
3 |
8 |
4 |
5 |
=(
1 |
5 |
4 |
5 |
3 |
8 |
=1+
3 |
8 |
=1
3 |
8 |
(3)
8 |
9 |
2 |
3 |
1 |
3 |
=
8 |
9 |
2 |
3 |
1 |
3 |
=
8 |
9 |
1 |
3 |
=
5 |
9 |
点评:本题的这三种方法都是常用的简算方法,要会灵活运用.
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