Learn about Classification of Polygons In this lesson, let’s learn how we classify polygon which means how we name them. Just to refresh our memory, a polygon is a two-dimensional figure that has a closed path. It is made up of straight lines only or line segments but it has to have more than three or more straight line segments would have to make up a polygon. So let’s look at this one. Well it’s a close figure and we know it’s a polygon. It’s made up of how many lines? One, two, three, four, five, six, and seven. Polygons are named based on number of lines. Since we’ve got 7 lines, it’s called a heptagon. A heptagon has got 7 lines. “Hepta” is 7. This one has--one,two, three, four, five, six, seven, eight lines, it’s an octagon which is “Octo” is eight. So remember, seven lines heptagon, 8 lines octagon. Let’s look at the other ones. But before we move on, both of these are not regular polygons. Why do we call them not regular? Because the lengths of all the sides are not the same, the sides and angles are not the same size. As you can notice, this side is longer than this side, so the angles also are shaped differently. Let’s look at the bottom three figures. This has got three sides. All the angles are the same. All side lengths are the same. This is called a triangle. “Tri” stands for three and this is a regular polygon. This one has one, two, three, four, five sides all exactly the same length. That’s called a pentagon and it’s a regular pentagon. This one is four sides. Four sides are called a quadrilateral. And if all four sides and all four angles are equal, this is actually a square. So a polygon which is regular, a quadrilateral is just four sides because this is a regular polygon which is a regular quadrilateral. We call it a square—pentagon, triangle.