y=(ax-b)/(ax+b)
y(ax+b)=ax-b
axy+by=ax-b
(ay-a)x=-by-b
x=(-by-b)/(ay-a)
=b(y+1)/a(1-y)
反函数为y=b(x+1)/a(1-x)
x≠1 ,a≠0