A rule of the thumb that can be employed to test whether a relation defines a function, especially when the relation is one that relates between the set of real numbers is called the vertical line test. On the graph of the relation, draw vertical lines. A relation \(f\) is a function if and only if every vertical line cuts the graph of \(f\) at most once.

A rule of the thumb that can be employed to test whether a relation defines a function, especially when the relation is one that relates between the set of real numbers is called the **vertical line test**.

On the graph of the relation, draw vertical lines.  

A relation \(f\) is a function if and only if every vertical line cuts the graph of \(f\) **at most once**.

Vertical Line Test

Functions

International Baccalaureate Higher Level Mathematics

Vertical line test

Vertical line test