（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y
=（x+y)（x-y)-y^2+（x-y)^2-2y（3x^2-xy)÷2y
=（x+y)（x-y)-y^2+（x-y)^2-（3x^2-xy)
=（x+y)（x-y)+（x-y)^2-y^2-（3x^2-xy)
=[（x+y)+（x-y)]（x-y)-y^2-（3x^2-xy)
=2x(x-y)-y^2-（3x^2-xy)
=2x^2-2xy-y^2-3x^2+xy
=-x^2-xy-y^2
=-(x^2+y^2+xy)
=-(x^2-2xy+y^2+3xy)
=-[(x-y)^2+3xy]
=-[3^2+3*(-2)]
=-(9-6)
=-3
x=-1,y=2,代入可得3
（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y
=x²-y²-y²+x²+y²-2xy-3x²+2xy
=-x²-y²+2xy-2xy
=-[(x-y)²+2xy]
=-[9-4】
=-5
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