Remembering the PI angles

Question

What is a good way to remember the essential angles from the unit circle? For instance $$\cos\left(\frac{\pi}{4}\right)=\frac{\sqrt{2}}{2} \text{ and } \sin\left(\frac{\pi}{4}\right)=\frac{\sqrt{2}}{2}$$

Answer 1

In my opinion the most effective way is to memorize the important ones in the first quadrant and then obtain the others by symmetry.