tell whether f(X) = sin is an identity

Question

How to tell whether or not an equation is an identity, and how to prove identities.

For example, is f(X) = (sin² x + Cos² x) / Csc x an identity, and how can you tell?

Answer 1

??????????????? wether or not ????????????

the werd is IF

Answer 2

f(x) is a function which is defined by what follows the equals sign.

In this example f(x) is defined as sin(x) because the numerator contains an identity which can be replaced by 1. When the denominator is inverted it becomes sin(x). So we don’t have an identity but rather a definition. f(x) can be defined in many different ways, so it isn’t an identity.