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Shapes and angles

Sal explains how to identify the angles on different shapes and then draw shapes based on their number of angles. Created by Sal Khan.

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Video transcript

- [Narrator] In this video, we're gonna talk about shapes and something called angles, which you've might have heard the word before. So the first question is what is an angle? Well let me draw a shape and that might help explain what an angle is. So I'm gonna draw a triangle, and you might already know that a triangle has three sides. You can see one side, two sides, three sides, but it also has three angles. Now, what are the angles? Well for a shape like this, you can think of an angle as where two of the sides come together. So for example, this right over here is an angle because two of the sides have come together there, this side and this side come together at that point. So that's an angle. This is another angle. And that's another angle. So not only does a triangle have three sides, it also has three angles. Now let me ask you a question. If I had a rectangle like this, how many angles does it have? Pause this video and think about it. Well, we can see the angles. We have one angle here, another angle here, so two, three and four. So not only does a rectangle have four sides, it also has four angles. Now what if I were to give you another four-sided figure another quadrilateral, quadrilateral's a very fancy word, but it really just means four-sided figure, but one that's not a rectangle. What if I were to give you something like this? So this type of a quadrilateral, it still has four sides, but you can see that it looks a little bit different than a rectangle, I can do it so it's pretty straight. It still has one, two, three, four sides. How many angles do we have? And this figure is called a trapezoid. How many angles does a trapezoid have? Well, let me count them again. So we have one angle right over here, two, three, and four. So this quadrilateral, this trapezoid, like a rectangle, has both four sides and four angles. Now, if I were to go the other way around, if I were to ask you to draw a figure, and if you have pencil and paper I encourage you to do it, try to draw a shape that has five angles and see if you know the name for that shape. All right, now let's try to do this together and let me do this in a fun color, watch I'll do it in purple. So that is one angle right over there, then I have two angles, then I have three angles, and now I have four angles. And if I meet there, I get five angles. So we could see the angles here. I have one, two, three, four, five angles here. You also might see that I have one, two, three, four, five sides. And what do we call a five sided figure? We call that a pentagon. This is a pentagon right over here. So five angles and we had five sides. And so you could imagine if I had six angles, what type of a figure would it be? Well, I might not even draw it, you could draw it on paper if you like, but if you had six angles, you're going to have a hexagon, which is a six sided figure.