3/2x²y=(3/2)x²y ?3x²y-[2xy²-2（xy-(3/2)x²y)+xy]+3xy²=3x²y-[2xy²-2xy+3x²y+xy]+3xy²=3x²y-2xy²+2xy-3x²y-xy+3xy²=xy²+xy=xy(y+1)=3*(-1/3)*(-1/3+1)=-2/3
