Fórmulas de Ángulo Mitad

\begin{align} \sin \tfrac{\alpha}{2} &= \pm \sqrt{\tfrac{1 - \cos \alpha}{2}} \\ \\ \cos \tfrac{\alpha}{2} &= \pm \sqrt{\tfrac{1 + \cos \alpha}{2}} \\ \\ \tan \tfrac{\alpha}{2} &= \pm \sqrt{\tfrac{1 - \cos \alpha}{1 + \cos \alpha}} \\ \end{align}