### 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.