若1/x -1/y =3,求(2x+3xy-2y)/(x-y-2xy)
问题描述：
若1/x -1/y =3,求(2x+3xy-2y)/(x-y-2xy)
答
1/x -1/y =3
y-x/xy=3
y-x=3xy
x-y=-3xy
所以
(2x+3xy-2y)/(x-y-2xy)
=[2(x-y)+3xy]/(x-y-2xy)
=[2(-3xy)+3xy]/(-3xy-2xy)
=-3xy/-5xy
=3/5
答：(2x+3xy-2y)/(x-y-2xy)值为3/5.