# Question Video: Identifying Perpendicular Lines Mathematics • 3rd Grade

Determine the colours of the lines that are perpendicular to each other.

02:23

### Video Transcript

Determine the colours of the lines that are perpendicular to each other.

First, we need to ask the question what does perpendicular mean? What is the definition of perpendicular lines? Perpendicular lines intersect at a right — 90-degree — angle. We need to figure out which of these two lines will intersect at a right angle. To do that, let’s extend these lines out a little bit further.

We have an intersection of the blue and black line and we have an intersection of the blue and yellow line. Which one of these is a perpendicular intersection? One thing that we can do is take something that we know is 90 degrees and use it to measure each of these angles. Here’s my ruler. I know that the edge of my ruler is a 90-degree angle, is a right angle. So I’m going to use it to try and measure each of these angles.

Here’s what it looks like to measure the blue and yellow intersection and here’s what it looks like to measure the blue and black intersection. The blue and black intersection measures exactly 90 degrees. It is a right angle.

In the blue and yellow intersection, there is a space between the ruler and the angle. This tells us that the angle we’re measuring here is larger than 90 degrees and cannot make a perpendicular intersection.

The final answer is that the blue line and the black line are perpendicular to each other.