Versine

The versine or versed sine is a trigonometric function found in some of the earliest trigonometric tables. The versine of an angle is 1 minus its cosine. The versine or versed sine is a trigonometric function found in some of the earliest trigonometric tables. The versine of an angle is 1 minus its cosine. There are several related functions, most notably the coversine and haversine. The latter, half a versine, is of particular importance in the haversine formula of navigation. The versine or versed sine is a trigonometric function already appearing in some of the earliest trigonometric tables. It is written as versin(θ), sinver(θ), vers(θ), ver(θ) or siv(θ). In Latin, it is known as the sinus versus (flipped sine), versinus, versus or the sagitta (arrow). Expressed in terms of the meanwhile more commonly used 'vertical' sines (sinus rectus) and cosines (cosinus rectus) functions, the versine is equal to 1 − cos(θ), or 2 sin2(θ/2).