Question

先化简在求值;(-1/3XY)²×[xy(2x-y)-2x(xy-y)²],其中X=-2/3,Y=2

我算的是-7 求正确答案
如果错了求过程

Answer 1

(-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]
=1/9x²y²×[2x²y-2x³y²+4x²y²-3xy²]
=1/9x³y³×[2x-2x²y+4xy-3y]
=1/9×(-2/3)³×2³×[2×(-2/3)-2×(-2/3)²×2+4×(-2/3)×2-3×2]
=1/9×（-8/27）×8×[-4/3-16/9-16/3-6]
=-64/3×(-130/9)
=8320/27

追问

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)]

追答

不对，是：
(-1/3xy)²×[xy(2x-y)-2x(xy-y)²]
=1/9x²y²×[2x²y-xy²-2x(x²y²-2xy²+y²)]

Answer 2

(-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]
=1/9x²y²×[2x²y-2x³y²+4x²y²-3xy²]
=1/9x³y³×[2x-2x²y+4xy-3y]
=1/9×(-2/3)³×2³×[2×(-2/3)-2×(-2/3)²×2+4×(-2/3)×2-3×2]
=1/9×（-8/27）×8×[-4/3-16/9-16/3-6]
=-64/3×(-130/9)
=8320/27

追问

过度的模仿是笨蛋

追答

呵呵，看出来了