Constant Function

Some especially important functions are the constant functions, the identity function, and the absolute value function.

A real number is sometimes called a constant. This name is used to emphasize the difference between a fixed real number and a variable.

For a given real number c, the function f with the rule

f(x) = c

is called the constant function with value c. It has domain R and range {c}.

The function f given by the rule

f(x) = x

is called the identity function.