__Right triangle trigonometry____Non-right triangle trigonometry____Trigonometric equivalencies____Hyperbolic functions____Contributors__

A *right triangle* is defined as having one angle precisely equal to 90^{o} (a *right angle*).

H is the *Hypotenuse*, always being opposite the right angle. Relative to angle x, O is the *Opposite* and A is the *Adjacent*.

"Arc" functions such as "arcsin", "arccos", and "arctan" are the complements of normal trigonometric functions. These functions return an angle for a ratio input. For example, if the tangent of 45^{o} is equal to 1, then the "arctangent" (arctan) of 1 is 45^{o}. "Arc" functions are useful for finding angles in a right triangle if the side lengths are known.

Note: all angles (x) must be expressed in units of *radians* for these hyperbolic functions. There are 2π radians in a circle (360^{o}).

Contributors to this chapter are listed in chronological order of their contributions, from most recent to first. See Appendix 2 (Contributor List) for dates and contact information.

**Harvey Lew** (??? 2003): Corrected typographical error: "tangent" should have been "cotangent".

*Lessons In Electric Circuits* copyright (C) 2000-2015 Tony R. Kuphaldt, under the terms and conditions of the Design Science License.