化简求值:[x(x2y2-xy)-y(x2-x3y)]÷3x2y,其中x=3,y=-1.

问题描述:

化简求值:[x(x2y2-xy)-y(x2-x3y)]÷3x2y,其中x=3,y=-1.

原式=[x3y2-x2y-x2y+x3y2]÷3x2y
=(2x3y2-2x2y)÷3x2y
=

2
3
xy-
2
3

当x=3,y=-1时,
原式=
2
3
×3×(-1)-
2
3
=-
8
3