The Big Square Root Trick for Remembering the Unit Circle

I learned this "trick" at an APSI several years ago.  I know lots of people use the "hand trick", and I do teach that to my students, but I like this trick better because I can write it down on paper and "see" what I'm doing a little easier.  I taught it in Pre-Cal and I review it in AP Calculus.  I tell the students who take the AP Exam that the first thing they should do when they get their test is write this down.  If you combine it with a trick for remembering what's positive in each of the four quadrants of the unit circle, they can evaluate most any trig function on the test.

Drawing the Square Root:

Using the Square Root: