问题
解答题
先化简代数式（
|
答案
原式=（
-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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先化简代数式（
|
原式=（
-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．