Positive and negative angles. Measuring angles in radians and in degrees and conversion from one measure to another. Definition of trigonometric functions with the help of unit circle. Truth of the identity sin^{2}x + cos^{2}x = 1, for all x. Signs of trigonometric functions. Domain and range of trigonometric functions and their graphs. Expressing sin (x Â± y) and cos (x Â± y) in terms of sin x, sin y, cosx and cos y. Deducing the identities like the following: