若x-y/x+y=5
则x-y=5(x+y)
所以求x-y/2x+2y+5x+5y/3x-3y
=5(x+y)/[2(x+y)]+5(x+y)/3(x-y)
=5/2+5(x+y)/[3*5(x+y)]
=5/2+1/3
=17/6