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Basic Geometry

Basic Geometry

At a Glance - Polygons

A polygon is any closed figure with three or more straight sides. "Closed" means that there are no gaping holes in it and that all sides connect together.

These Are Polygons:


These Are Not Polygons:


That's right, a circle is not a polygon. It doesn't have all the properties, and it's really hard to count the number of sides.

Names of Some Common Polygons

Number of SidesNumber of AnglesName
77Septagon (or Heptagon)

Important Vocabulary

Polygons have a lot of important vocabulary terms that come with them. You will need to memorize these, but don't worry, they aren't too difficult.

  • Angle: the shape formed when two rays meet at a common point. AKA "the corner."
  • Vertex: the point where two rays meet; the corner point of a polygon. The plural of vertex is vertices. 
  • Side: the straight edge of a polygon.

Angle Side Vertex Polygons

  • Equiangular: a figure where all angles are equal in measure.
  • Equilateral: a figure where all sides are equal in length.
  • Regular Polygon: an equilateral, equiangular polygon. 

Regular Polygons

You're probably familiar with these shapes


These Are Not Regular

Non-regular Polygons

Base and Height of a Polygon

  • Base: the bottom side of a polygon.
  • Height: the height of a polygon is the perpendicular distance from the top-most vertex to the base. The height and base ALWAYS form a right angle.

Height and Base Polygons

Exercise 1

Which of the following look like regular polygons?

Regular Polygons?

Exercise 2

How many vertices does the following polygon have?

7 vertice polygon

Exercise 3

Which two sides form the height and base of the polygon?

ABCD Polygon