A(z1), B(z2),C(z3) are the vertices of a triangle ABC inscribed in the circle |z|=2. Internal angle bisector of the angle A, meet the circumcircle again at D(z4) then:
z42=z2z3
z4=z2z3z1
z4=z1z2z3
z4=z1z3z2
∠BAD=∠CAD ⇒arc BD=arc CD
⇒ ∠BOD=∠COD=A
z4z2=eiA=z3z4
⇒z42=z2z3