题目内容
计算1999×
.
| 1997 |
| 1998 |
1999×
,
=(1998+1)×
,
=1998×
+1×
,
=1997+
,
=1997
.
| 1997 |
| 1998 |
=(1998+1)×
| 1997 |
| 1998 |
=1998×
| 1997 |
| 1998 |
| 1997 |
| 1998 |
=1997+
| 1997 |
| 1998 |
=1997
| 1997 |
| 1998 |
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