Vertical line test

Alternative definition of function. A function $f$ with domain $ D$ can be viewed as the set

$\displaystyle W = \{(x, f(x)): x \in D\}

of points $ (x, f(x))$ on the rectangular coordinate system.

Vertical line test. Every ``vertical line'' should intersect the graph of $f$ in at most one point.

Department of Mathematics
Last modified: 2005-09-29