Math Open Reference
Math Open Reference: Irregular Polygon
A complete reference guide to irregular polygons. It provides definitions and an interactive activity that enhances further explanation. Includes links to related topics.
ClassFlow
Class Flow: Polygons
[Free Registration/Login Required] This flipchart defines a polygon and the classification of concave and convex polygons.
National Council of Teachers of Mathematics
The Math Forum: Plane Figure
This site provides a definition for plane figure (at the top of the page) and a few examples.
University of Georgia
University of Georgia: Inter Math: Nonagon
This site gives the general definition of a nonagon with examples of a regular (convex) and irregular concave nonagons. There are links to related terms, challenging problems, more information, and the interactive check point involving...