Functions that perform trigonometric operations, such as cosine, sine, and tangent.

The ratios between sides of a triangle: sine {sin} (the side opposite the angle over the hypotenuse), cosine {cos} (the side adjacent to the angle over the hypotenuse), and tangent {tan} (opposite over adjacent); and their inverses: secant {sec} (hypotenuse over opposite), cosecant {cosec} (hypotenuse over adjacent), and cotangent {cot} (adjacent over opposite). (See Construction and Use of a Sundial and Observations Using a Gnomon)

A function (sine, cosine, tangent, cotangent, secant, cosecant) whose independent variable is an angle measure, usually in degrees or radians.

Originally, the names given to the 6 possible ratios between pairs of sides in a right-angled triangle (sine, cosine, tangent, cotangent, secant, cosecant). Usually the triangle is drawn with resting on one of its shorter sides, and these functions are viewed as depending on the bottom acute angle (angle smaller than 90 degrees). Later the definitions were extended for any angle, using the unit circle. Though initially introduced as a tool of land-surveying, today trigonometric functions play a key role in many areas of mathematics.

sin == opposite hypotenuse cos == adjacent hypotenuse tan == opposite adjacent cot = tan = sec = cos = csc = sin = sin = cos = tan = cot = tan = sec = cos = csc = sin