 You should already know that the x-axis goes in this direction and the y-axis goes in this direction but if you've forgotten, watch part 1 first. In this video, we're going to look at the equation of horizontal and vertical lines. So let's start with vertical lines. Have a look at this line here. All of the points on this line have an x-coordinate of 3. So we can say that the equation of this line is x equals 3. So what do you think the equation of this line would be? Pause the video, work out the answer and click play when you're ready to check. Hopefully you thought x equals negative 5 because all of the points on the line have an x-coordinate of negative 5. So what do you think the equation of this horizontal line will be? Pause the video, have a think and click play when you're ready to check. Did you think it was y equals 6? Because all of the points on the line have a y-coordinate of 6, hence y equals 6. So that is horizontal and vertical lines but there are two important diagonal lines. This one and this one. Notice the coordinates on this line. So when x is 1, y is 1 and when x is 4, y is 4. The x and y coordinates are always the same. This means the equation of the line is y equals x. So what about this line? It isn't y equals x because the coordinates aren't exactly the same. Notice how when x is negative 2, y is positive 2. And when x is negative 5, y is positive 5. So what do you think the equation of this line would be? Pause the video, have a think and click play when you're ready to check. Did you think y equals negative x? Well done if you did. So when x is negative, y is positive, hence y equals negative x. So from this video you should be able to find the equation of any vertical line, any horizontal line and these two diagonal lines.