若x+2y分之x-y=3,则代数式x+2y分之2（x-y)-3(x-y)分之x+2y的值为
问题描述：
若x+2y分之x-y=3,则代数式x+2y分之2（x-y)-3(x-y)分之x+2y的值为
答
(x-y)/(x+2y)=3
2(x-y)/(x+2y)-(x+2y)/(3(x-y))
=2*[(x-y)/(x+2y)]-1/(3*[(x-y)/(x+2y)])
=2*3-1/(3*3)
=6-1/9
=5又8/9