【1/2x的2次方y的3次方-(-2xy)(-xy的2次方)+(-5x的2次方y)的3次方】除2xy=【1/2x^2y^3-2x^2y^3-125x^6y^3】除2xy=2xy/【xy(1/2xy^2-2xy^2-125x^5y^2)】=2/(-3/2xy^2-125x^5y^2)=-4/(3xy^2+250x^5y^2)...