已知xy=-2,x-y=3,求(x+y)(x-y)-y平方+(x-y)平方-（6x2y-2xy平方）/2y的值
问题描述：
已知xy=-2,x-y=3,求(x+y)(x-y)-y平方+(x-y)平方-（6x2y-2xy平方）/2y的值
答
(x+y)(x-y)-y^2+(x-y)^2-(6x^2y-2xy^2)/(2y) =X^2-y^2-y^2+X^2+y^2-2xy-3x^2+xy =-x^2-y^2-xy =-(x^2+y^2+xy-3xy+3xy) =-(x-y)^2-3xy =-9+6 =-3