This video lecture from Trigonometric Identities (F.Sc. first year Mathematics) covers: Question numbers 11-12 of exercise 10.2. In these questions we are given with the information that alpha, beta and gamma are three angles of a triangle then we prove the given trigonometric equation. Find more e-learning material and educational video lectures in Urdu at maktab.pk. These videos are free to use for promotional and commercial purpose by keeping the credits to Maktab.