If , prove that, = a + b a +…

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

Problem

\tan \frac{\theta}{2} = \sqrt{\frac{a-b}{a+b}} \tan \frac{\phi}{2}

, prove that,

\cos \theta = \frac{a \cos \phi + b}{a + b \cos \phi}