An interactive applet and associated web page that define and describe the radius of a regular polygon. The applet has a polygon where the user can change the umber of sides and alter the radius by dragging a vertex. The radius is shown with it's length changing accordingly. The web page has formulae for the length of the radius given the number of sides and the apothem or side length.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.