WEBVTT
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Angles
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In this video, we’re going to learn how to identify and name acute angles, right angles, and obtuse angles.
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An angle is the amount of turn between two straight lines or rays, which meet at a vertex or point.
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We call the sides of an angle the arms.
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We measure angles in degrees, and this is the symbol we use to write degrees.
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A complete turn is 360 degrees.
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And if we make half a turn, we’ve turned 180 degrees.
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And a quarter of a turn is 90 degrees.
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Angles which have a square corner, like this angle, are called right angles.
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A right angle measures 90 degrees.
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An angle which measures less than 90 degrees is called an acute angle.
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An angle which measures more than 90 degrees but is less than a straight line is called an obtuse angle.
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You could have a go at making some angles of your own.
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You could use craft pipe cleaners.
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Which angle have we made?
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It’s a right angle.
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Can you see it has a square corner?
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Which kind of angle is this?
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It’s less than a right angle.
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Can you remember its name?
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It’s an acute angle.
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This angle is greater than a right angle.
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Can you remember its name?
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It’s an obtuse angle.
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We can tell if an angle is acute or obtuse by comparing it to a right angle.
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We can make our own right-angle corner using a piece of paper.
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And we can use this to check if an angle is less than or greater than a right angle.
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First, we need to fold the piece of paper in half and then fold it in half again.
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We’ve made a right-angle measure.
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We can use our right-angle measure to tell if an angle is greater than or less than a right angle.
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This angle is greater than a right angle, which means it’s an obtuse angle.
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By matching the corner of our right-angle measure with the vertex of this angle, we can see the angle measures less than a right angle.
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So, we know that this is an acute angle because acute angles measure less than a right angle.
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Let’s try some questions now to help us practice identifying acute angles, right angles, and obtuse angles.
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Determine the type of angle highlighted in orange.
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Is it a right angle, an obtuse angle, or an acute angle?
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In this question, we have to identify the type of angle which is highlighted in orange.
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Is this angle a right angle?
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We could use a right-angle measure to check.
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We simply need to place the corner of our right-angle measure into the corner or vertex of the angle.
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Now, we can see the orange angle measures more than a right angle.
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What do we call an angle which is greater than a right angle?
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Can you remember what an obtuse angle is?
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This is an obtuse angle.
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It measures more than a right angle.
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The angle highlighted in orange measures more than 90 degrees, so it’s an obtuse angle.
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Acute angles measure less than a right angle.
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The type of angle highlighted in orange is an obtuse angle.
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Determine the type of angle highlighted in orange.
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Is it a right angle, an obtuse angle, or an acute angle?
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In this question, we have to identify which type of angle the orange angle is.
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Is this angle a right angle?
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We’ve drawn the arms of the angle.
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This is a right angle.
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The orange angle is less than a right angle.
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An obtuse angle is an angle which measures greater than 90 degrees.
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The orange angle is not an obtuse angle.
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The angle highlighted in orange is an acute angle.
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It measures less than a right angle.
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The type of angle highlighted in orange is acute.
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The orange angle is an acute angle.
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Which of these is an acute angle?
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Angle 𝐴, angle 𝐵, or angle 𝐶.
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In this question, we have to identify the acute angle.
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It can’t be angle 𝐵 because it’s a right angle.
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This is the symbol we use to show a right angle.
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We need to use our knowledge of angles to help answer this question.
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We know that an acute angle is less than a right angle.
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Does angle 𝐴 or angle 𝐶 measure less than a right angle?
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We could use a right-angle measure to help.
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Angle 𝐴 measures less than a right angle.
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The angle which is an acute angle is angle 𝐴 because it measures less than a right angle.
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Angle 𝐵 is a right angle, and angle 𝐶 is greater than a right angle.
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Angle 𝐴 is an acute angle.
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Look at the given shape.
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How many acute angles are there in the shape?
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How many obtuse angles are there in the shape?
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How many right angles are there in the shape?
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In this question, we have to count the number of acute angles in the given shape, the number of obtuse angles, and the number of right angles.
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We can answer the third part of the question really quickly.
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This blue square is the symbol we use to show a right angle, so we know the shape has one right angle.
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How many acute angles are there?
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We know acute angles measure less than 90 degrees or less than a right angle.
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This is an acute angle, and this is an acute angle.
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Both of these angles measure less than a right angle.
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This angle is greater than a right angle.
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We call this type of angle an obtuse angle.
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So, there are two acute angles, one obtuse angle, and one right angle in the given shape.
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What have we learned in this video?
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We’ve learned how to identify right angles using a right-angle measure.
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We’ve learned that acute angles measure less than a right angle.
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And we’ve learned that obtuse angles are greater than a right angle.