Trigonometry/Some Little-known Trigonometric Functions

There are some further trigonometric functions that are found occasionally. Few people use them, but it avoids confusion if you know what they are.

The chord of an angle θ is the length of a line joining the ends of two radii of a circle of radius 1, and separated by θ. Equivalently, it is the base of an isosceles triangle where the equal sides are of length 1 and the angle between them is θ.

${\text{chord}}(\theta )=2\sin \left({\frac {\theta }{2}}\right)$

The versed sine of an angle, vers(θ) = 1-cos(θ).

The haversine or half versed sine of an angle,

${\text{havers}}(\theta )={\text{hav}}(\theta )={\frac {1}{2}}(1-\cos(\theta ))=\sin ^{2}\left({\frac {\theta }{2}}\right)$.

The coversed sine of an angle, covers(θ) = 1-sin(θ).