Figure 1: Concave Polygon 

Figure 1 is an example of a concave polygon. Note that part of the line between the
two points in the figure lie outside the polygon.

Figure 2: Convex polygon 

Figure 2 is an example of a
convex
polygon. Note that the entire line is
contained
within the polygon. In fact, a line drawn between any two points that are part of the
polygon will be entirely contained within the polygon.


A polygon is a
closed
shape whose boundaries consist of straight lines. A polygon is concave if, for
any two points that are part of the shape, a straight line can be drawn between
the two points that lies outside the shape.^{[1]} A property of
concave polygons is that if the sides are extended, the extension of at least two sides will intersect
one of the other sides. Also, a polygon is concave if any of the interior angles is greater than 180°.
Click on the blue points and drag them to change the figure.
If an angle at a vertex is a straight line, and all the other angles are less than 180 degrees, is the polygon concave or convex?
 Manipulative 1  Concave Polygon Created with GeoGebra. 
