y=a/c(x+b/a)/(x+d/c)=a/c [(x+d/c-d/c+b/a)/(x+d/c)]=a/c[1+(b/a-d/c)/(x+d/c)]=a/c+(bc-ad)/[c^2(x+d/c)]当bc-ad0时,其中心点为：(-d/c, a/c)当bc-ad=0时,函数分子分母约分,退化为常数函数y=a/c....