Trigonometry is developed to solve geometric problems involving triangles. Chapter “Trigonometric Functions” discusses positive and negative angles, method of measuring angles in radians as well as in degrees and conversion from one measure to another. The chapter also deals with the definition of Trigonometric Functions with the help of unit circle, general solution of trigonometric equations, signs, domain and range of Trigonometric Functions and their graphs. The chapter helps the students in learning the process of expressing sin (x±y) and cos (x±y) in terms of sinx, siny, cosx & cosy along with their simple applications and deducing the identities, related to sin 2x, cos 2x, tan 2x, sin 3x, cos 3x and tan 3x.