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's because$$\cos(x-360^\circ)=\cos(x)\text{ and }\sin(x-360^\circ)=\sin(x).$$
