Trigonometry is the mathematics of triangles and trigonometric functions, also defined as the study of the relationships of lines and angles in the triangle.

### Recommended Resources

Presenting an introduction and a guide to trigonometry, useful for learning a bit about the subject, or for brushing up. The brief online courses include its applications, background, angle measurement, chords, sines, cosines, tangents and slope, right angles, trigonometric functions, the trigonometry of oblique triangles, and others.

http://www.clarku.edu/~djoyce/trig/

Free Trigonometry Tutorials and Problems

Provides free tutorials and help in solving trigonometric equations, and formulas, using Java applets to interactively explore such things as trigonometric functions, sine law, and inverse trigonometric functions.

http://www.analyzemath.com/Trigonometry.html

Offers illumination on the topic of trig, and explains such things as functions and labeling sides. Also contains cosine, sine, and tangent calculators.

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

Lays out the basics of trigonometry including sines, cosines, slopes, oscillations, waves, and triangles.

http://oolong.co.uk/trig.htm

Featured here are interactive online calculators that can assist in learning triangle geometry by drawing shapes and displaying formulas as the learner enters angles, side lengths, depths and other variables.

http://www.visualtrig.com/

Wolfram Math World: Trigonometry

Expounds upon trigonometry as well as such things as the Pythagorean theorem, Osborn's rule, and the Euler formula.

http://mathworld.wolfram.com/Trigonometry.html