成立 设a/b=c/d=k≠1 则a=bk c=dk 所以(a+b)/(a-b) =(bk+b)/(bk-b) =b(k+1)/b(k-1) =(k+1)/(k-1) (c+d)/(c-d) =(dk+d)/(dk-d) =d(k+1)/d(k-1) =(k+1)/(k-1) 所以(a+b)/(a-b)=(c+d)/(c-d)
