Dictionary Definition
The Oxford English Dictionary defines a polygon as "a plane figure with many (usually more than four) straight sides and the same number of angles."Regular Polygons
Regular polygons have sides of equal length and equal angles.| Shape | Name | Number of sides |
|---|---|---|
 |
Triangle (or Trigon) A regular triangle is an equilateral triangle | 3 |
 |
Quadrilateral (or Tetragon) A regular quadrilateral is a square | 4 |
 |
Pentagon | 5 |
 |
Hexagon | 6 |
 |
Heptagon | 7 |
 |
Octagon | 8 |
 |
Nonagon | 9 |
 |
Decagon | 10 |
 |
Dodecagon | 12 |
Irregular Polygons
Irregular polygons have sides of different lengths and different angles.| Shape | Name | Number of sides |
|---|---|---|
 |
Irregular Quadrilateral | 4 |
 |
Irregular Hexagon | 6 |
 |
Irregular Octagon | 8 |
What's in a Name?
Polygon comes from the Greek 'poly-', meaning "many", and '-gon', meaning "angle". Therefore 'polygon' means "many angles" as each polygon has several angles inside of it.Interior Angles
The angles between the sides in a polygon, inside the shape, are called interior angles.
There is a formula for the sum of the interior angles of a polygon:
In this formula, n is the number of sides of the polygon.
For example, a hexagon has 6 sides, so n = 6. Putting this into the formula gives:
Sum of interior angles = (n − 2) × 180°
Sum of interior angles = (6 − 2) × 180°
Sum of interior angles = 4 × 180°
Sum of interior angles = 720°
Exterior Angles
The angles between the sides in a polygon, outside the shape, are called exterior angles.
The exterior angles always add up to 360°.
This page was written by Stephen Clarke.
You might also like...
geometryunderstanding explementary anglesunderstanding the interior angles of a polygonfinding the interior angle of a regular polygon
Help Us Improve Mathematics Monster
- Do you disagree with something on this page?
- Did you spot a typo?
Find Us Quicker!
- When using a search engine (e.g., Google, Bing), you will find Mathematics Monster quicker if you add #mm to your search term.
Share This Page
If you like Mathematics Monster (or this page in particular), please link to it or share it with others.
If you do, please tell us. It helps us a lot!
Create a QR Code
Use our handy widget to create a QR code for this page...or any page.
