-½x²×(2xy²-4x²y²)-4x²y×(-xy),其中x=2 y=-1........................

-½x²×(2xy²-4x²y²)-4x²y×(-xy),其中x=2 y=-1........................
-½x²×(2xy²-4x²y²)-4x²y×(-xy),其中x=2 y=-1
........................

-½x²×(2xy²-4x²y²)-4x²y×(-xy),其中x=2 y=-1........................
-½x²×(2xy²-4x²y²)-4x²y×(-xy)
=-x³y^2+2x^4y^2+4x^3y^2
=3x^3y^2+2x^4y^2
将x=2 y=-1带入
原式=3*8*1+2*16*1=24+32=56