When y is a function of x, then one value of y associated with one value of x from the domain of the function. This relationship is denoted by y = f (x), which is read as " y is equal to f of x " and it means that y is a function of x. Such a formula is called the functional notation.
For example, if y = 5 x + 11 then we can write this function as the notation f (x) = 5 x + 11.
Functional notation is used to find the value of y or f (x) associated with a certain value of x. If the function y = f (x) = 2 x – 5 is given, then for the values of x = 2, 5, or 8 we can find the corresponding values of y or f (x) by replacing them in the functional notation.