A Trigonometric identity is an identity that contains the trigonometric functions sin, cos, tan, cot, sec or csc. Trigonometric identities can be used to: Trigonometric identities can be used to: They can be easily replaced with derivations of the more common three: sin, cos and tan. cosecant can be derived as the reciprocal of sine: The inverse cosecant function - arccsc. For every trigonometry function such as csc, there is an inverse function that works in reverse. These inverse functions have the same name but with 'arc' in front.