If a relation is a function, each input has ONLY 1 OUTPUT!
This relation is NOT A FUNCTION. Slide to see why.
How it works ?
Recall the following definitions:
A relation is a correspondence between 2 sets. Algebraically, you can think of a relation as a set of ordered pairs (x,y).
Once special type of relation is called a FUNCTION. Every function is a relation, but not every relation is a function.
A function is a relation for which each and every input gets mapped to ONE and ONLY ONE output. The following applets help further illustrate this concept for functions represented graphically.