题目抄漏了,-2x应该是-2xy
1/x+1/y=3
(x+y)/(xy)=3
x+y=3xy
(4x-2xy+4y)/(x+xy+y)
=[4(x+y)-2xy]/[(x+y)+xy]
=(4·3xy-2xy)/(3xy+xy)
=(10xy)/(4xy)
=5/2