A polygon is a plane shape with straight sides.
Is it a Polygon?
Polygons are 2-dimensional shapes. They are made of straight lines, and the shape is "closed" (all the lines connect up).
|Not a Polygon
(has a curve)
|Not a Polygon
(open, not closed)
Polygon comes from Greek. Poly- means "many" and -gon means "angle".
Types of Polygons
Regular or Irregular
A regular polygon has all angles equal and all sides equal, otherwise it is irregular
Concave or Convex
A convex polygon has no angles pointing inwards. More precisely, no internal angle can be more than 180°.
If any internal angle is greater than 180° then the polygon is concave. (Think: concave has a "cave" in it)
Simple or Complex
A simple polygon has only one boundary, and it doesn't cross over itself. A complex polygon intersects itself! Many rules about polygons don't work when it is complex.
(this one's a Pentagon)
(also a Pentagon)
(a "star polygon",
in this case a pentagram)
Play With Them!
Try Interactive Polygons ... make them regular, concave or complex.
Names of Polygons
|If it is a Regular Polygon...|
|Triangle (or Trigon)||3||60°|
|Quadrilateral (or Tetragon)||4||90°|
|Heptagon (or Septagon)||7||128.571°|
|Nonagon (or Enneagon)||9||140°|
|Hendecagon (or Undecagon)||11||147.273°|
|n-gon||n||(n-2) × 180° / n|
You can make names using this method:
Example: a 62-sided polygon is a Hexacontadigon
BUT, for polygons with 13 or more sides, it is OK (and easier) to write "13-gon", "14-gon" ... "100-gon", etc.
A Quad Bike has 4 wheels
The "Pentagon" in Washington DC has 5 sides
Think Hexagon is a "Six-agon"
An Octopus has 8 tentacles
Think Nonagon is a "Nine-agon"
Think Decagon has 10 sides,
just like our Decimal system has 10 digits