计算题:(x+2y)(x-y)-(x+y)^2

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计算题:(x+2y)(x-y)-(x+y)^2计算题:(x+2y)(x-y)-(x+y)^2计算题:(x+2y)(x-y)-(x+y)^2(x+2y)(x-y)-(x+y)^2=x^2-xy+2xy-

计算题:(x+2y)(x-y)-(x+y)^2
计算题:(x+2y)(x-y)-(x+y)^2

计算题:(x+2y)(x-y)-(x+y)^2
(x+2y)(x-y)-(x+y)^2
=x^2-xy+2xy-2y^2-x^2-2xy-y^2
=-xy-3y^2

(x+2y)(x-y)-(x+y)^2
=(x^2-xy+2xy-2y^2)-(x^2+2xy+y^2)
=x^2-xy+2xy-2y^2-x^2-2xy-y^2
=-xy-3y^2