RADIANS
Helpful Links
Video explanation: http://www.youtube.com/watch?v=9zspW8u6kQM
http://math.rice.edu/~pcmi/sphere/drg_txt.html
http://www.intmath.com/Trigonometric-functions/7_Radians.php
http://en.wikipedia.org/wiki/Radian
http://en.wikipedia.org/wiki/File:Degree-Radian_Conversion.svg
http://id.mind.net/~zona/mmts/trigonometryRealms/radianDemo1/RadianDemo1.html
http://mathworld.wolfram.com/Radian.html