
[2x的平方-(x+y)(x-y)][(2-x)(x+2)+(-y-2)(2-y)],其中x=-1,y=二分之一
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[2x的平方-(x+y)(x-y)][(2-x)(x+2)+(-y-2)(2-y)]
=(2x^2-x^2+y^2)(4-x^2+y^2-4)
=(x^2+y^2)(y^2-x^2)
=y^4-x^4
=(1/2)^4-(-1)^4
=1/16-1
=-15/16
=(2x^2-x^2+y^2)(4-x^2+y^2-4)
=(x^2+y^2)(y^2-x^2)
=y^4-x^4
=(1/2)^4-(-1)^4
=1/16-1
=-15/16
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