先化简再求值(a的5次方-2a的4次方-4a的三次方)/(-1/2a的三次方)a=-1 -x(3xy-6x的平方y的平方)/(3x的平方)

(a^5-2a^4-4a^3)/(-1/2a^3) a=-1
=(a^2-2a-4)/(-1/2)
=-2(a²-2a-4)
=-2(1+2-4)
=-2(-1)
=2
-x(3xy-6x²y²)/(3x²)
=-(y-2xy²)
=2xy²-y