So, if I have an angle, say it's 135o, that simplified would be 45o right? But if I have an angle, say 330o, it simplifies to 30o rather than 60o? Why?
Here is a page with some pretty and interactive diagrams (if you scroll down a bit) that may help you.
https://www.mathsisfun.com/algebra/trigonometry.html
Take a look at what happens if you put the angle at 135 degrees and at 330 degrees. You will see the acute angle ath must be used.
Let me know how you get on.