Activities in Math: Trigonometry [ Teens/Mature Teens ] - Three comprehensive modules from Syvum. Each includes theory and explanation, along with practice exercises. http://www.syvum.com/math/trigonometry.html

Addition Formulas for Sines and Cosines [ Teens/Mature Teens ] - Describes how the Sine and Cosine Addition Formulas can be derived by using vectors and how these formulas can be remembered relatively easily. http://www.pitt.edu/~wek3/sineadd/node1.html

An Index of Trigonometry Help Pages [ Teens/Mature Teens ] - Provides detailed discussion of trigonometry concepts. Includes examples of varying difficulty. http://www.hyper-ad.com/tutoring/math/trig/

An Introduction to Trigonometry [ Teens/Mature Teens ] - Definitions, basics, functions, and other concepts necessary to understand basic trigonometry. http://www.ping.be/~ping1339/gonio.htm

Basic Trigonometry [ Mature Teens ] - Cosine, sine and tangent are defined. The Pythagorean theorem is illustrated as well the number of degrees in a many sided figure. http://abe.www.ecn.purdue.edu/~agen215/trig.html

Dave's Short Trig course [ Teens/Mature Teens ] - Covers basic definitions and concepts in beginning trigonometry. http://aleph0.clarku.edu/~djoyce/java/trig/

Four Branches of Trigonometry [ Mature Teens ] - Includes information on the laws of sines and cosines, right triangle trigonometry, and the ambiguous case. http://geocities.com/lilvballbabe23

GCSE Maths: Trigonometry [ Teens ] - Explains right triangle properties, historic background, the Pythagorean theorem, and trigonometric functions. Includes definition of terms and illustrations. http://www.gcse.com/maths/trigonometry.htm

S.O.S. Math - Trigonometry [ Mature Teens ] - Covers measuring degrees, equations, and formulas. Includes illustrations and related links. http://www.sosmath.com/trig/trig.html

Sine and Other Trigonometric Functions [ Mature Teens ] - Interactive tests and exercises. http://answermath.com/sin.htm

Trigonometry [ Teens/Mature Teens ] - Introduction to trigonometry. Includes links to trig-based animations and definitions. http://fergusmurray.members.beeb.net/trig.htm