a /b=c/d
则a/c=b/d
a/c-1=b/d-1
(a-c)/c=(b-d)/d
c/(a-c)=d/(b-d)
c/(a-c)+0.5=d/(b-d)+0.5
0.5(a+c)/(a-c)=0.5(b+d)/(b-d)
(a+c)/(a-c)=(b+d)/(b-d)
a /b=c/d
则a/c=b/d
a/c-1=b/d-1
(a-c)/c=(b-d)/d
c/(a-c)=d/(b-d)
c/(a-c)+0.5=d/(b-d)+0.5
0.5(a+c)/(a-c)=0.5(b+d)/(b-d)
(a+c)/(a-c)=(b+d)/(b-d)