题目内容：

已知x分之1减去y分之1等于2 求2x-3xy-2y分之3x+7xy-3y等于多少

优质解答

1/x-1/y=2
y-x=2xy
x-y=-2xy
(3x+7xy-3y)/(2x-3xy-2y)
=[3(x-y)+7xy]/[2(x-y)-3xy]
=[-6xy+7xy]/[-4xy-3xy]
=xy/[-7xy]
=-1/7