Video: Naming Polygons with a given Number of Sides and Angles

Name the shape that matches this description. [A] It has 5 sides. [B] It has 5 angles. [C] It is closed.

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Video Transcript

Name the shape that matches this description. It has five sides. It has five angles. It is closed.

In this question, we’re being asked to identify the name of a shape based on some information that we’ve been given. What clues do we know? Let’s start by highlighting the important information in the problem.

We’re told that the shape has five sides. It has five angles. And we’re also told that it’s a closed shape. Let’s think about what each of those clues mean.

Now the sides of a shape are the lines that are used to make it. So we know that this shape is formed from five lines. Here’s an example of a shape with five sides: one, two, three, four, five.

When we talk about the angles of a shape, we usually mean the angles inside the shape, unless we say otherwise. These are the angles between each side, and they’re found in each of the vertices or corners of the shape. So let’s count the angles in the vertices of this five-sided shape that we’ve drawn: one, two, three, four, five. So our shape has five sides and five angles.

And our final clue is that the shape is closed. This means that there are no gaps in between any of the sides of the shape. If we take our pencil around the sides of the shape, we’ll arrive back where we started without having to jump across any gaps. So we can see that that’s true and that there are no gaps. It’s a closed shape.

So this shape has five sides, five angles, and is closed. But what is its name? Now knowing where different words come from is important in maths. It can really help us understand what mathematical words mean. For example, another word for a 2D shape is a polygon, which is made up of two word roots. “Poly” means many, and “gon” means angles or angled, a many-angled shape, a polygon. But do you know the word root that means “five” so that we can use it for a five-angled shape? Well, the word root “penta” means five. And so the name of a shape that has five sides, five angles, and is closed is a pentagon.

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