问题
解答题
先化简，再求值：当x=2，y=-1时，求
|
答案
原式=
-xy2 x2-y2
•x4y (x2-y2)•(x2+y2) x2+y2 x2
=
-xy2 x2-y2 x2y x2-y2
=xy2-x2y x2-y2
=xy(y-x) (x-y)(x+y)
=-xy x+y
原式=-
=2．2×(-1) 2+(-1)
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先化简，再求值：当x=2，y=-1时，求
|
原式=
-xy2 x2-y2
•x4y (x2-y2)•(x2+y2) x2+y2 x2
=
-xy2 x2-y2 x2y x2-y2
=xy2-x2y x2-y2
=xy(y-x) (x-y)(x+y)
=-xy x+y
原式=-
=2．2×(-1) 2+(-1)
