Circular Functions

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:

$\displaystyle \cot x$	$\textstyle \equiv$	$\displaystyle {1\over\tan x}={\cos x\over \sin x}$	(1)
$\displaystyle \csc x$	$\textstyle \equiv$	$\displaystyle {1\over\sin x}$	(2)
$\displaystyle \sec x$	$\textstyle \equiv$	$\displaystyle {1\over\cos x}$	(3)
$\displaystyle \tan x$	$\textstyle \equiv$	$\displaystyle {\sin x\over\cos x}.$	(4)

The study of circular functions is called Trigonometry.

References

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.