已知xy/x+y=2,求代数式3x-xy+3y/-x+3xy-y的值

问题描述:

已知xy/x+y=2,求代数式3x-xy+3y/-x+3xy-y的值

原式=(3x+3y-xy)/[3xy-(x+y)]
=[3(x+y)-xy]/[3xy-(x+y)]
=[3-xy/(x+y)]/[3xy/(x+y)-1]
=(3-2)/(3×2-1)
=1/5