已知x分之1减y分之1等于3,则代数式x-xy-y分之5x+xy-5y的值是?

1/x-1/y=3 得y-x=3xy
∴xy=(y-x)/3
则x-xy-y=x-y-(y-x)/3=4(y-x)/3
5x+xy-5y=5(x-y)+(y-x)/3=14(x-y)/3
∴(5x+xy-5y)/(x-xy-y)
=[14(x-y)/3]/[4(y-x)/3]
=-14/4=-7/2