A function f from a set A to the same set A is said to be an identity function if f(x) = x for all x ∈ A i.e. f : A → A is defined by f(x) = x for all x ∈ A. Identity function is denoted by I_{A} or I. Therefore, I(x) = x always.

**Graph of Identity Function**

The graph of the identity function f(x) = x is the graph of the function y = x. It is the straight line y = x.