This video lecture from Fundamentals of Trigonometry (F.Sc. first year Mathematics) covers: Question numbers 13-24 of exercise 9.4. In these questions we prove the given trigonometric identities and find the domain of angle in each case. 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.