IM pretty sure you don't go about it with domain -180 \le \theta \le 180
this is my working for a solution, correct me if its wrong
{ tan }^{ 2 }3\theta=1
{ tan }3\theta=\sqrt{1} so for values 0 \le \3theta \le 1080
{ tan }3\theta= +-{1}
3\theta= 45 degrees this is your basic angle
so do the...