A **polygon** is a plane figure formed by three or more line segments. The points where the sides meet are called **vertices**, and sum of the lengths of a polygon’s sides is its **perimeter**. If all of the sides and angles of a polygon are equal, it is called a **regular polygon**. In the diagram below, both shapes are *hexagons*, but the one on your left is a *regular*, while the one on the right is **irregular**. Equal sides or angles are illustrated with daggers **|**.

The simplest of all polygons is a **triangle**. It has three sides and the total sum of its interior angles is 180°. In this section, you’ll learn how to calculate the sum of the interior angles of any polygon. The formula that’s used to calculated the total sum is:

**Sum of Angles**

null

Where **S **represents the total sum and **n** represents the number of sides. Let’s take a look at four different examples in increasing difficulty.