(x+y)(x-y)-y²+(x-y)²-(6x²y-2xy²)÷2y
=x^2-y^2-y^2+x^2-2xy+y^2-3x^2+xy
=-x^2-y^2-xy
=-(x-y)^2-3xy
=-3^2-3*(-2)
=-3