先化简再求值:(x+y)(x-y)+(x^2-2xy+y^2)-(x^2y)^3÷(x^2y)^2,其中x=1,y=2.
问题描述：
先化简再求值:(x+y)(x-y)+(x^2-2xy+y^2)-(x^2y)^3÷(x^2y)^2,其中x=1,y=2.
答
(x+y)(x-y)+(x^2-2xy+y^2)-(x^2y)^3÷(x^2y)^2
=x²-y²+x²-2xy+y²-x²y
=2x²-2xy-x²y
当x=1,y=2时
原式=2-4-2
=-4