=-1/3ab(2a^2b-4ab+ab^2)=-2/3a^3b^2+4/3a^2b^2-1/3a^2b^3=a^2b^2(-2/3a+4/3-1/3b)把a=-1又1/2 即a=-3/2,b=-2代入原式,得=（-3/2）^2(-2)^2[(-2/3)*(-3/2)+4/3-1/3*(-2)]=9/4*4[1+4/3+2/3]=27