已知x+y分之xy=2,求-x+3xy-y分之3x-5xy+3y的值
问题描述：
已知x+y分之xy=2,求-x+3xy-y分之3x-5xy+3y的值
答
x+y分之xy=2,
则
xy/(x+y)=2
xy=2x+2y
(-x+3xy-y)分之(3x-5xy+3y)
=(3x-5xy+3y)/(-x+3xy-y)
=[3x-5(2x+2y)+3y)/[-x+3(2x+2y)-y]
=(3x-10x-10y+3y)/(-x+6x+6y-y)
=(-7x-7y)/(5x+5y)
=[-7(x+y)]/[5(x+y)]
=-7/5
=-1.4