列竖式计算．580+7200=8010﹣4500=380+56=
用递等式计算．（1）（2）（3）．
+ + ++ ﹣ ﹣++ ﹣﹣ 1﹣++﹣．
计算：= 1﹣= = = == = 1﹣= = =
+=﹣==改正：
用推算计算（1）+=（2）﹣=
．
+
+
+
+
﹣
﹣
+
+
﹣
﹣
1﹣
+
+
﹣
．
= 1﹣
= 
= 
= 
=
= 
= 1﹣
= 
= 
=
+
﹣
+
=
﹣
=
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