A polygon is a many-sided close figure. Memorize the following terms:
- 3 sides: triangle
- 4 sides : quadrilateral
- 5 sides : pentagon
- 6 sides : hexagon
- 7 sides : heptagon
- 8 sides : octagon
- 9 sides : nonagon
- 10 sides: decagon
Regular Polygons
When a polygon’s angles are all equal and its sides are all equal, it is called regular. Examples of regular polygons are equilateral triangles ( a regular triangle) and squares ( a regular quadrilateral)
Sum of Exterior Angles
The exterior angles of any polygon add up to 360 degrees.
Interior Angles
The interior angles of any quadrilateral add up to 360 degrees. To find the interior angles of any other polygons. Use the following formula:
(Number of sides minus by 2) multiplied by 180: (n – 2) 180. Since you know that 180 is the number of degrees in a triangle you are simply finding how many triangles there are in the figure then multiplying that by 180. Note in the figure that a pentagon can be divided into 3 triangles (number of sides, 5 minus 2, equals 3) which are each 180o for a total of 540 degrees.