In mathematics, an identity function, also called an identity relation or identity map or identity transformation, is a function that always returns the same value that was used as its argument. In equations, the function is given by f(x) = x.
If x and y are the came set and if for each x = X ; F(x) = X, we say that f is an identity function of x.
The domain of function of real variable may be describe implicitly by an equation used to define a function.
Generally, it can be represented diagrammatically as;
And the Graph as;