1/4x的3次方y的2次方*(-2xy的2次方)+(-2x的2次方y)*(-1/2xy)*3x的2次方y的2次方z
=1/4x^3y^2*(-2xy^2)+(-2x^2y)*(-1/2xy)*3x^2y^2z
=-1/2x^4y^4+x^3y^2*3x^2y^2z
=-1/2x^4y^4+3x^5y^4z