(-1/3xy)²×[xy(2x-y)-2x(xy-y)²]=1/9x²y²×[2x²y-xy²-2x(x²y²-2xy²+y²)]=1/9x²y²×[2x²y-xy²-2x³y²+4x²y²-2xy²]...第二步算错了应该是(-1/3xy)²×[xy(2x-y)-2x(xy-y)²]=1/9x²y²×[2xy-xy-2x(x²y²-y²)]不对，是：(-1/3xy)²×[xy(2x-y)-2x(xy-y)²]=1/9x²y²×[2x²y-xy²-2x(x²y²-2xy²+y²)]