Trigonometry/Some Little-known Trigonometric Functions

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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 equilateral 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).