What is a polygon?
A polygon is a flat, closed shape made of straight sides. Triangles, squares, pentagons and hexagons are all polygons, but circles are not, because they have curved edges.
The word polygon comes from Greek words meaning many angles. A polygon must have at least three sides, joined end to end so the shape is closed. Each corner where two sides meet is called a vertex. Polygons are named by their number of sides, such as quadrilateral for four, heptagon for seven and decagon for ten.
In a regular polygon, all sides and angles are equal, like a square or an equilateral triangle. Irregular polygons have sides or angles of different sizes. Convex polygons have all corners pointing outward, while concave polygons have at least one corner pointing inward, like a star.
Angles in a polygon
The interior angles of any polygon can be found with a simple rule: subtract 2 from the number of sides and multiply by 180 degrees. A triangle has 180 degrees, a square 360 and a hexagon 720. This works because any polygon can be split into triangles.
Did You Know?
Computer graphics in video games and animated films build 3D objects from millions of tiny polygons, usually triangles.