（1/X）-（1/Y）=3
(y-x)/xy=3
y-x=3xy
x-y=-3xy
(2X+3XY-2Y)/(X-2XY-Y)
=[2(x-y)+3xy]/[(x-y)-2xy]
=(-6xy+3xy)/(-3xy-2xy)
=-3xy/-5xy
=3/5