information:extraction
Version suited to small angles

When the angle, γ, is small and the adjacent sides, a and b, are of similar length, the right hand side of the standard form of the law of cosines is subject to catastrophic cancellation in numerical approximations. In situations where this is an important concern, a mathematically equivalent version of the law of cosines, similar to the haversine formula, can prove useful:

In the limit of an infinitesimal angle, the law of cosines degenerates into the circular arc length formula, c = a γ.