z=（1+根号3i/1-根号3i）^2
z=（1+√3i/1-√3i）^2={（1+√3i）*（1+√3i）/【（1-√3i）*（1+√3i）】}^2=(-1/2+√3i)^2=-1/2-√3i/2
|z| =1