先化简在求值2(x-y)平方-(y-x)平方-(x+y)(y-x)其中x=3,y=-2

题目

先化简在求值2(x-y)平方-(y-x)平方-(x+y)(y-x)其中x=3,y=-2

答案

2(x-y)²-(y-x)²-(x+y)(y-x)
=[2(x-y)+(y-x)][(x-y)-(y-x)]
=(x-y)(2x-2y)
=2(x-y)²
=2×[3-(-2)]²
=2×5²
=2×25
=50
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