# Function Fun, Relations

- Author:
- Dr. Doug Davis, 3D

Not all curves are functions. This applet shows a few curves that are or are not functions. The primary test for a function is the vertical line test. If more than one value exist for any value, the resulting value cannot be determined. A curve that is not a function still represents a relation. Examples are shown in the applet.
Click the next button to advance to the next relation.
For the last relation, five black points can be used to modify the relation.

For each relation move the value and note the domain and range of the relations that are functions.
All of the relations in this applet are conic sections, can you have other types of relations that are not functions?