Definition of: trigonometric functions

Certain functions of an angle or arc used in trigonometry. The most commonly used are: sine, cosine, tangent, cotangent, secant, cosecant. In illustration A the functions of the angle θ are defined as ratios or fractions. They are:
TRIGONOMETRIC FUNCTIONS

sine θ =	cosecant θ =
cosine θ =	secant θ =
tangent θ =	cotangent θ =

The functions may be represented also as lines by constructing the reference triangle in a circle whose radius is taken as unity, and drawing additional lines as in B. The sine is then AB, the cosine CB, the tangent ED, the cotangent GF, the secant CE, and the cosecant CF. These are all spoken of as the sine, cosine, etc., of the arc AD as well as of the angle θ. Other, less common, trigonometric functions are: versed sine, coversed sine, exsecant, and haversine. These functions are expressed as follows:
versed sine θ (or versine θ) = 1 - cosine θ coversed sine θ (or versed cosine θ) = 1 - sine θ
exsecant θ = secant θ - 1
haversine θ =1/2 versine θ