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)