Tangent

A line that meets a smooth curve at a single point and does not cut across the curve.

Or

A trigonometric function. The trigonometric function of angle A is defined as:

Note: In this series A is in radians and

The following expression is also known as the half angle formula:

See also: Cosecant, Cosine, Cotangent, Secant, Series Expansions, Sine.