1. Polygons

2. What is a Polygon?
A polygon is a closed figure that is the union of line segments in a plane. 
A polygon has three or more sides.
A polygon has the same number of angles as sides.

3. Concave or Convex
  * In a convex polygon, each interior angle measures less than 180 degrees. 
*Concave polygons "cave-in" to their interiors, creating at least one interior angle greater than 180 degrees.

4. Regular or not Regular
A polygon is regular if all the sides and angles are equal in measure

5. Types of Polygons Polygon Graphic Sides Angles Triangles Degrees
Diagonals
(from one vertex)
Triangles
Degrees

6. Polygon
Graphic
Sides
Angles
Diagonals
Triangles
Degrees

7. Polygon
Graphic
Sides
Angles
Diagonals
Triangles
Degrees

8. Interior Angles
Sum of Interior Angles of a Polygon= 180(n - 2) (where n = number of sides)
Example 1:  Find the number of degrees in the sum of the interior angles of an 14 – sided polygon.
Example 2: Find the number of degrees in the sum of the interior angles of an 20 – sided polygon,

9. Interior Angles To find missing angles in a polygon
1. Find the total number of degrees in polygon.
2. Set up an equation equal to the number of degrees.
3. Solve equation.

10. Example
87°
99°
99° x°
105°

11. Interior Angles Each interior angle of a regular polygon =
where n = the number of sides in the polygon
Example 1: Find the number of degrees in each interior angle of a regular dodecagon.
Example 2: Each interior angle of a regular polygon measures 135°.  How many sides does the polygon have?

12. Find the value of x. 9x 9x
12x
12x 9x 9x

13. Exterior Angles
An exterior angle of a polygon is an angle that forms a linear pair with one of the angles of the polygon.
For the hexagon shown at the left, <1 and <2 are exterior angles for that vertex. 
Formula: Sum exterior angles of any polygon = 360° (using one exterior angle at a vertex)
Formula:  Each exterior angle (regular polygon) = 1 2

14. Exterior Angles Example 1: Find the sum of the exterior angles of:
1. pentagon
2. decagon
3. a 15 sided polygon
4. a 7 sided polygon
* Example 2: Find the measure of each exterior angle of a regular hexagon.