Trigonometry/Some Little-known Trigonometric Functions< Trigonometry
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.
The versed sine of an angle, vers(θ) = 1-cos(θ).
The haversine or half versed sine of an angle,
The coversed sine of an angle, covers(θ) = 1-sin(θ).