If , then prove that one of values of is…

MATHEMATICS · Subjective · A Level · Mathematics · Trigonometry · Trigonometry

Problem

\cos \theta = \frac{\cos \alpha + \cos \beta}{1 + \cos \alpha \cos \beta}

, then prove that one of values of

\tan \frac{\theta}{2}

\tan \frac{\alpha}{2} \tan \frac{\beta}{2}