解；m-n=b/a-(2a+b)/(a+b) =b/a-a/(a+b)-1 =(ab-b²-2a²-ba)/[a(a+b)] =(-b²-2a²)/[a(a+b)] =-(b²2a²)/[a(a+b)] 因为a,b都是有理数,所以：m-n