http://www.sosmath.com/algebra/solve/solve0/solvtrig.html

http://www.sosmath.com/trig/trig.html

http://www.calculus.net/ci2/search/?request=category&code=114&off=0&tag=9200438920658

http://www.karlscalculus.org/calc7_0.html

http://www.math.com/homeworkhelp/Trigonometry.html

http://www.ping.be/~ping1339/gonio.htm

http://w3.fiu.edu/math/cine_math/fast/trigonometry/trigonometry.htm

http://www.hyper-ad.com/tutoring/math/trig/