（12x^3y^4-15x^2y^3+2分之1x^2y^2）除以-(4x^2y)
=（12x^3y^4-15x^2y^3+1/2x^2y^2）*1/(-4x^2y)
=-3xy^3+15/4y^2-1/8y
=-1/8y(24xy^2+30y-1)