3/2x^3y^2-4yx+1/2y^2x^3-1/2xy-3x^3y^2-y^2x^3
=(3/2x^3y^2-3x^3y^2)+(-4yx-1/2xy)+(1/2y^2x^3-y^2x^3)
=-3/2x^3y^2-9/2xy-1/2y^2x^3