(2x+y)(x-y)-(2x+y)(y-2x)+(2x^2y-y)^2/(-y^2)
=(2x+y)(x-y-y+2x）+[(2x^2-1)*y]^2/(-y^2)
=(2x+y)(3x-2y)-(2x^2-1)^2
=6x^2-xy-2y^2-4x^4+4x^2-1
=10x^2-xy-2y^2-4x^4-1