\begin{definition}[Definition:Haversine]
The '''haversine''' of an angle is defined as:
{{begin-eqn}}
{{eqn | l = \hav \theta
      | r = \dfrac 1 2 \paren {1 - \cos \theta}
      | c = 
}}
{{eqn | r = \dfrac 1 2 \vers \theta
      | c = where $\vers \theta$ denotes the versed sine of $\theta$
}}
{{eqn | r = \sin^2 \dfrac {\theta} 2
      | c = Double Angle Formula for Cosine: Corollary 2
}}
{{end-eqn}}
\end{definition}