原式=-3x*(2x²-x+4)=-6x^3+3x²-12x5/2xy×（﹣x³y²+5/4x²y³)5/2xy×（﹣x3y2+5/4x2y3)=-5/2x2y+25/8xy2x(2/1x+1)-3x(2/3x-2)1/2+x-2x2+6x=-2x2+7x+1/2