Graphing Horizontal & Vertical Lines
Before we get into the complexities of graphing lines, we are going to first introduce how to graph the really simple lines, those that are completely vertical or horizontal.
Take a look at these lines:
What do you notice about all of these horizontal lines? If you answered that they are all y = something, then you’re right.
Horizontal lines are all in y = A form, where A is any real number.
This is because you are graphing all points where y equals some number. Let's look at y = 3 a little more closely.
If we pick any point on the line, like the three shown, the y-coordinate will be 3. The x-coordinate will vary, but the y will always be 3. That's why the equation for this line is y = 3.
Now take a look at these lines:
Have you noticed that these lines were all vertical – and in the form x = something? Not surprisingly, this is because all points that lie on a vertical line have the same x-coordinate.
Here are some points on the line x = -1:
If we want to graph the line y = -2, all we need to do is plot all the points that have a y-coordinate of -2 and connect them, sort of like connect the dots.
We didn't really need to graph all of those points, two would have been sufficient, but we like to make a point (no cheesy math pun intended).