How do we recognize functions?

A Relation is a set of ordered pairs. The set of ordered pairs in a relation can be shown using braces, tables, graphs, and mappings. 

A Function is a relation that assigns exactly one output value (range/y-value) for each input value (domain/x-value).

Recognize functions by making sure the same input value (x) is NEVER repeated. 

Some characteristics of a function are:
1. Each x-value must be matched with a y-value
2. Some y-values may not be matched with a x-value
3. Two or more x-values may be matched with the same y-value
4. A x-value CANNOT be matched with 2 different y-values.