a=-5/3
b=-2/5
(a+2b)/(a-2b)
=((-5/3)-4/5)/(-5/3+4/5)
=(-37/15)/(-13/15)
=37/13对的吗?这也太简单了接题意得出ab值，代入计算就可以了，当然简单了。thank you.亲