题目可能有错,应该是(1/x)－(1/y)=5
1/x-1/y=5,
通分（y-x）/xy=5
x-y=-5xy
(3x+4xy-3y)/(2x-3xy-2y)
=[3*(x-y)+4xy]/[2*(x-y)-3xy]
=[3*(-5xy)+4xy]/[2*(-5xy)-3xy]
=(-11xy)/(-13xy)
=11/13