1.6. Classifying Polygons http://www.ck12.org
Diagonals:Line segments that connects the vertices of a convex polygon that are not sides.
The red lines are all diagonals.
This pentagon has 5 diagonals.
Example 8:Determine if the shapes below are convex or concave.
Solution: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.
Example 9:How many diagonals does a 7-sided polygon have?
Solution:Draw a 7-sided polygon, also called a heptagon. Drawing in all the diagonals and counting them, we see
there are 14.