[tex] \frac{(1 + \cos( \alpha ))(1 - \cos( \alpha ) ) }{ \sin {}^{2} ( \alpha ) } = \frac{1 - \cos {}^{2} ( \alpha ) }{ \sin {}^{2} ( \alpha ) } = \frac{ \sin {}^{2} ( \alpha ) }{ \sin {}^{2} ( \alpha ) } = 1[/tex]