2002 HSC help (1 Viewer)

[mathpie]

Hi, this is Question 7 b from the 2002 HSC. I could do parts (i) - (iii) pretty easily but I'm struggling with (iv). I understand the solution up until it says "so OP3 = |z4| = 1". How do they know that OP3 = 1?? Also, can the exterior angle sum of a polygon be 4pi, 6pi, etc and not just 2pi?
Question:
Solution:

 

[dan964]

Hi,
According to the question pre-amble.
You are given in CIS form, .
This means that
Given that .