计算 (x-y)²-(x+y)(x-y)
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计算 (x-y)²-(x+y)(x-y)
计算 (x-y)²-(x+y)(x-y)
计算 (x-y)²-(x+y)(x-y)
(x-y)²-(x+y)(x-y)=x²+y²-2xy-(x²-y²)
=x²+y²-2xy-x²+y²
=2y²-2xy
(x-y)²-(x+y)(x-y)
=(x-y)(x-y-x-y)
=-2y(x-y)
原式=(x²-2xy+y²)-(x²-y²)
=x²-2xy+y²-x²+y²
=-2xy+2y²