http://www.ck12.org Chapter 1. Basics of Geometry
TABLE1.1:(continued)
Polygon Name Number of Sides Number of Diagonals Convex Example
Dodecagon 12?n−gon n(wheren>12)?Example A
Which of the figures below is a polygon?
The easiest way to identify the polygon is to identify which shapes are not polygons.BandCeach have at least one
curved side, so they cannot be polygons.Dhas all straight sides, but one of the vertices is not at the endpoint of the
adjacent side, so it is not a polygon either.Ais the only polygon.
Example B
Determine if the shapes below are convex or concave.
To see if a polygon is concave, look at the polygons and see if any angle “caves in” to the interior of the polygon.
The first polygon does not do this, so it is convex. The other two do, so they are concave. You could add here that
concave polygons have at least one diagonal outside the figure.