Definition: We say that a number $f(b)$ is a maximum value for $f$ on a set  D, if whenever $a \in D$ , $f(a) \le f(b)$.
We say that a number $f(b)$ is a minimum value for $f$ on a set  D, if whenever $a \in D$ , $f(a) \ge f(b)$.
We say that a number $f(b)$ is an extreme value for $f$ on a set  D, if $f(b)$ is a maximum value for $f$ on a set  D or $f(b)$ is a minimum value for $f$ on a set  D
 Graph Mapping Diagram Maximum: If $a \in D$ then $f(a) \le f(b)$. Minimum: If $a \in D$ then $f(a) \ge f(b)$.