题目内容
先化简代数式（
-
）÷
，然后请你任意选取一组x、y的值代入求值．（所取的x、y值要保证原代数式有意义）
| x2-y2 |
| x2-y2 |
| x-y |
| x+y |
| 2xy |
| (x-y)2(x+y) |
原式=（
-
）÷
=
÷
=
×
=x-y，
选取x=2，y=1，∴原式=2-1=1．
| x2-y2 |
| (x+y)(x-y) |
| (x-y)2 |
| (x-y)(x+y) |
| 2xy |
| (x-y)2(x+y) |
=
| x2-y2-(x-y)2 |
| (x+y)(x-y) |
| 2xy |
| (x-y)2(x+y) |
=
| 2xy |
| (x-y)(x+y) |
| (x-y)2(x+y) |
| 2xy |
=x-y，
选取x=2，y=1，∴原式=2-1=1．
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