**Define and identify relations and functions**

Since we can write related quantities using ordered pairs, a set of ordered pairs such as

{(5, 40), (10, 80), (20, 160), (40, 320)}

is called a *relation*.

**Relation**

A **relation **is any set of ordered pairs.

A special kind of relation, called a *function, *is very important in mathematics and its applications.

**Function**

** **

A **function **is a relation in which, for each value of the first component of the ordered pairs, there is *exactly one value *of the second component.