Just to add, this is the link to the unit circle java applet, you may find it very helpful,
http://www.wou.edu/~burtonl/trig.html
This is a link to an online lesson on unit circles, it could help if your having trouble.
http://www.bmlc.ca/Math40S/Pre-Calculus%20Math%2040s%20-%20Trigonometry%20Lesson%202.pdf