The functions describing the horizontal and vertical positions of a point on a Circle as a function of Angle
(Cosine and Sine) and those functions derived from them:
See also Cosecant, Cosine, Cotangent, Elliptic Function, Generalized Hyperbolic Functions, Hyperbolic Functions, Secant, Sine, Tangent, Trigonometry
Abramowitz, M. and Stegun, C. A. (Eds.). ``Circular Functions.'' §4.3 in
Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing.
New York: Dover, pp. 71-79, 1972.