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Lesson Video: Angles and Right Angles Mathematics • 3rd Grade

In this video, we will learn how to recognize and define angles, identify right angles, and make angles that are bigger or smaller than a given angle.

09:17

Video Transcript

Angles and Right Angles

In this video, we will learn how to recognize and define angles, identify right angles, and say whether angles are bigger or smaller than a right angle. An angle is formed by two straight lines sharing an endpoint. We can also call an endpoint a vertex.

How many angles can you count in this shape? Here’s one angle. We’ve drawn the two lines that meet at a point to create this angle. Here’s our second angle. There’s a third angle and a fourth. This shape has four angles. How many angles does this triangle have? One, two, three. Did you notice that the word triangle contains the word angle? A triangle means a shape with three angles. The prefix tri- means three.

How many angles does this shape have? One, two, three, four. This shape has two special angles called right angles. A right angle is an angle that forms a square corner. Some angles, like this one, measure less than a right angle. And other angles, like this one, are bigger than a right angle. We can use a set square to help us identify right angles. We simply place the square corner of the set square into the angle we want to measure. If the square corner fits neatly inside the angle, as it does in this case, then we know the angle is a right angle because a right angle is an angle that forms a square corner.

If you don’t have a set square, you could make your own right angle tester using a piece of paper. All you need to do is fold your piece of paper in half, like so, and then fold it in half again. Now you have your very own right angle tester. Let’s practice using it to see if we can find any more right angles in our shape.

Our right angle tester fits really neatly into this angle. So we found another right angle in our shape. Our shape has two right angles. We can also use our right angle tester to test if an angle is bigger or smaller than a right angle. By placing our right angle tester in this angle, we can see that this angle is smaller than a right angle. And by placing our right angle tester into this angle, we can see the angle is bigger than a right angle. So we’ve learned that this shape has four angles. Two of these angles are right angles. One angle is bigger than a right angle. And the other is smaller than a right angle.

Let’s practice what we’ve learned about angles by answering some questions.

Which of the following shapes has four angles?

In this question, we’re shown four different shapes. We have to select the shape which has four angles. Let’s start by looking at this shape. We know angles are formed by two lines which share an endpoint. Here’s one angle, two, three. Our first shape has three angles. How many angles does this shape have? One, two, three, four, five. The shape has five angles. Let’s count the number of angles the third shape has. One, two, three, four, five, six. So this must be the shape which has four angles. Let’s quickly check. Yes, it does have four angles. This is the shape which has four angles.

Pick the shape that Emma is describing. “It has five angles. Three of the angles are right angles.”

In this question, we’ve been shown four different shapes. We have to pick the one which has five angles and three of those angles are right angles. Which of our shapes has five angles? Let’s count the number of angles the first shape has. Here’s one, two, three, four, five. Does this shape have three right angles? No, it doesn’t.

How many angles does our second shape have? A square has four angles. Emma’s looking for the shape which has five angles, and three of those angles should be right angles. This is not the shape that Emma is describing. How many angles does our third shape have? Here’s one, two, three, four, five. This could be the shape that Emma is describing.

Does it have three right angles? We can check using our right angle tester. A right angle is an angle that forms a square corner. So our shape has five angles, and we know that one of them is a right angle. Here’s a second right angle. Here’s another. This shape does have three right angles. So this is the shape that Emma is describing. It has five angles and three of the angles are right angles. This shape is a pentagon. It has five sides and five angles. But none of its angles are right angles. We picked the shape that Emma is describing. It has five angles and three of them are right angles.

Complete using “more” or “less”: The given angle is more or less than a right angle.

In this question, we have to compare the angle we’ve been given to a right angle. Is this angle more or less than a right angle? A right angle is an angle that forms a square corner. To help us decide if the given angle is more or less than a right angle, we could use this set square. This corner of the set square is a right angle. So if we place our set square into the angle we’ve been given, we can see if our angle is a right angle. There we go. The given angle is smaller than a right angle. So the missing word is “less.” The given angle is less than a right angle. We completed the sentence using the word less.

What have we learned in this video? We have learned that an angle is formed by two lines sharing an endpoint. We also learned that a right angle is an angle that forms a square corner. And finally, we learned how to tell if an angle is bigger or smaller than a right angle using a set square or a right angle tester.

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