Prosthaphaeresis Formulas/Sine plus Sine

Theorem

 * $\sin \alpha + \sin \beta = 2 \sin \left({\dfrac {\alpha + \beta} 2}\right) \cos \left({\dfrac {\alpha - \beta} 2}\right)$

where $\sin$ denotes sine and $\cos$ denotes cosine.

Also reported as
This result is also sometimes reported as:


 * $\dfrac {\sin \alpha + \sin \beta} 2 = \sin \left({\dfrac {\alpha + \beta} 2}\right) \cos \left({\dfrac {\alpha - \beta} 2}\right)$