Video: Identifying the Type of a Given Angle

The lines are perpendicular. What type of angle is highlighted in red?

02:11

Video Transcript

These lines are perpendicular. What type of angle is highlighted in red?

The first sentence in this question contains a really interesting word “perpendicular.” Now, we’re told that these lines are perpendicular, but which lines is it describing? Well, if we look in the picture, we can see two lines. We’ve got one that’s vertical that goes up and down. And we’ve also got a horizontal line that has been drawn from left to right. Now, what can we say about these lines? Well, firstly, we can see that they’re straight lines. They’re not curved at all, are they? We can also see that these two lines meet together. In fact, they cross over each other, don’t they?

Now, there are lots of ways we could draw two lines that cross over each other, like this or this. But the two lines in our picture are interesting because they meet in a special way. When two lines are perpendicular, we know that they meet at right angles. But imagine that we read this first sentence and we didn’t know what the word “perpendicular” means. Can you see another clue that helps us? This little symbol here is the symbol for right angles. So even if we’re not quite sure what the word “perpendicular” means, we could look at the diagram, see this little symbol, and think to ourselves, “I know that these two lines meet at right angles.”

Now, our question asks us, what type of angle is highlighted in red? Can you see what this is talking about? It’s this angle here. How could we describe this angle? Well, because we know that these two lines are perpendicular, we can draw little right-angle symbols at all the places where they meet. The angle that’s shown in red is a right angle. When two lines are perpendicular, they meet at right angles. And that’s how we know the type of angle that’s highlighted in red is a right angle.

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