DefinitionTrigonometric Identities are the expressions and equations which involve trigonometric functions, though are verified only for specific angles and so are true for all the right triangles, theoretical reasonings and declarations at only specific set of angles. Methods including decomposing, simplifying, forcing a common denominator, and using reciprocal, Pythagorean, and co-function identities. For Example: sin2(x)+cos2(x)=1 (Proved by Pythagorean identity.)