Vertical line test

Revision as of 13:33, 3 July 2006 by Inscrutableroot (talk | contribs) (proofreading)

The vertical line test states that:

A relation is a function iff no vertical line intersects the graph in more than one point.

For example, $y=x^2$ is a function because any vertical line intersects it in, at most, one point, while $x^2+y^2=1$ is not a function (try x=0).