# Names Of Polygons – 50 Easy Polygon Names

Names of Polygons are decided based on the number of sides it contains. A polygon is a closed plane figure made up of segments (also called sides). Polygons are named according to the number of segments from which they are comprised

The word “geometry” comes from the Greek geos which means “earth” and metron which means “measurement”. In this chapter we will learn the differences between polygons and polyhedrons and how to calculate various lengths (perimeters), areas, and volumes (in the case of the polyhedrons) of various geometric figures.

## Polygons: An Introduction

A polygon is a closed plane figure made up of segments (also called sides). Polygons are named according to the number of segments from which they are comprised. The term n-gon is used to denote a polygon with n sides. The n is substituted, according to the number of sides that
comprise the figure, by the Greek cardinal prefixes: penta (or 5), hexa (or 6), hepta (or 7), etc. The only two exceptions are the three- and four-sided polygons which are the triangles (never “trigons”) and quadrilaterals (never “tetragons”). The number of sides is equal to the number of
angles in all polygons.

Polygons can be classified in two different ways: internal angles and lengths of sides. Depending on the measure of the internal angles, polygons can be convex, with all internal angles less than 180° (see page 211), or concave (with at least one or more internal angles greater than 180°). You can distinguish a convex polygon from a concave polygon by noting that convex polygons have all their angles pointing out, while concave polygons have at least one angle that points inward. It is impossible to construct a 3-sided (triangular) concave polygon.

## Examples of Convex Polygons

Convex polygons can also be classified as regular (when they are equilateral―that is, all sides have the same length; and equiangular―that is, all angles have the same measure) and irregular (when at least one angle or side differs from the rest).

## Examples of Irregular Polygons

The parts that make up a polygon are the following:
Sides: the segments or straight lines that form the polygon.
Vertices: the point where the sides meet. The sides always form an angle at each vertex.
Diagonals: are the lines that join two non-consecutive angles.
Consider the following convex hexagon:

A “hexagon” is a 6-sided polygon having 6 vertices and 9 different diagonals. In general, the number of diagonals can be computed given the number of vertices, n, using this formula:

no. of diagonals = n(n – 3)/2

Diagonals that connect the vertices of a concave polygon, will sometimes lie partially or completely outside the boundaries of the object.

The polygons are named according to the number of sides they contain as given in the table below. In actual practice, instead of, for example, identifying a 40-sided polygon as a tetracontagon, most mathematicians will simply call it a 40-gon.

## Optional Formulas:

The sum of the interior angles of a general n-sided polygon is given by the following:

Sum of interior angles = (n – 2)180°

Given an interior angle, a, the exterior angle is 180 – a and the number of sides of a regular ngon having that interior angle is given by

n=360/180−a.

Knowing n, we can find a = 180 -(360/n).

The sum of the exterior angles of a polygon is always 360 degree.

## Polyhedrons: An Introduction

All polygons by definition are two-dimensional (i.e., flat) objects. Let´s consider now threedimensional figures (i.e., solid figures that have height, width, and depth).

A polyhedron is a geometric solid in three dimensions with flat faces and straight edges. A polyhedron is a three-dimensional figure assembled with polygonal-shaped surfaces. In a manner similar to that of polygons. Polyhedrons are comprised of
Faces: Plane polygon-shaped surfaces.
Edges: Intersections between faces.
Vertices: The vertices of the faces are the vertices of the polyhedron also. Three or more faces can meet at a vertex.

Interestingly, the number of vertices (V), edges (E), and faces (F) of a polyhedron are related according to this formula:

V – E + F = 2

Here are some examples of polyhedrons (or polyhedra):