(y-x)/xy=3
y/xy-x/xy=3
所以1/x-1/y=3
(3x-5xy-3y)/(x-2xy-y)分子分母同时除以xy
原式=(3/y-5-3/x)/(1/y-2-1/x)
=[3(1/y-1/x)-5]/[(1/y-1/x)-2]
=[3*(-3)-5]/(-3-2)
=-14/-5
=14/5