已知1/X-1/Y=3,求代数式3Y-XY-3X/X-XY-Y

问题描述:

已知1/X-1/Y=3,求代数式3Y-XY-3X/X-XY-Y

1/x-1/y=3 y-x=3xy
(3y-xy-3x)/(x-xy-y)=(9xy-xy)/(3xy-xy)=4

1/X-1/Y=3
(y-x)/xy=3
y-x=3xy
所以
3Y-XY-3X/X-XY-Y
=(9xy-xy)/(-3xy-xy)
=-2