(x^3+3x^2-2xy^2+1)+(-xy^2+x^2-2X^3+2)+(x^3-4x^2*y+3xy^2-8)
=x^3+3x^2-2xy^2+1-xy^2+x^2-2X^3+2+x^3-4x^2y+3xy^2-8
=4x^2-4x^2y-5