(-1/2x^3)*x^2*(4y)^2-(-2xy)^2.3x^3

(-1/2x^3)*x^2*(4y)^2-(-2xy)^2.3x^3

(-1/2x^3)*x^2*(4y)^2-(-2xy)^2.3x^3
=-1/2 x^5*16y^2-4x^2y^2*3x^3
=-8x^5y^2-12x^5y^2
=-20x^5y^2