Mathematics Archives
Math Archives: Visual Calculus: Functions
Use this site to find the defintion of a function. The site offers a discussion on the vertical line test, symbolic, numerical and verbal discussions on the definition of a function.
Windstream
Ojk's Precalculus Study Page: Functions
An introduction to the basic terminology of functions, including how to use the vertical line test on the graph of a relation as a means of testing whether or not it is a function.