a/b=m/n和b/c=p/q
a=bm/n c=bq/p
a:b:c=bm/n:b:bq/p=m/n:1:q/p
若 a/b=c/d
令 a/b=c/d=k
a=bk c=dk
a+c=k(b+d)
(a+c)/b+d)=k
(a+c)/(b+d)=a/b=c/d
a/b=m/n和b/c=p/q
a=bm/n c=bq/p
a:b:c=bm/n:b:bq/p=m/n:1:q/p
若 a/b=c/d
令 a/b=c/d=k
a=bk c=dk
a+c=k(b+d)
(a+c)/b+d)=k
(a+c)/(b+d)=a/b=c/d