\begin{definition}[Definition:Prosthaphaeresis/Trigonometry]
The trigonometric technique of prosthaphaeresis is based on the Prosthaphaeresis Formula for Sine plus Sine:
:$\dfrac {\sin \alpha + \sin \beta} 2 = \map \sin {\dfrac {\alpha + \beta} 2} \, \map \cos {\dfrac {\alpha - \beta} 2}$
\end{definition}