用z'代表复数z的共轭复数
则：z=a+bi z'=a-bi z*z'=a^2+b^2=1
|（z-a）/（a*z'-1）|
= |z（z-a）/（z*a*z' - z）| ……上下乘以z
= | z(z-a) / (a-z) |
= | -z |
= 1