Complex numbers $z=-3-4i$ polar form Let $z=-3-4i$ . In polar form this becomes $[5, 233° ]$. The question then asks for $z^2$, so the polar form becomes $[25,466]$ However in the solution they did $466° -360° $ and I am unsure why they did this. Is it a rule that needs to be applied. 

It is just to get the principal value of the angle, since if you rotate by an angle $466^{\circ}$ you'll get to the same position as rotating $106^{\circ}$ so we usually take the smallest angle that is needed to arrive at the desired position.
The principal angle is an angle between $-180^{\circ}$ and $+180^{\circ}$
