How to Graph Vertical and Horizontal Lines
The equation of any vertical line comes in the form
where “a” is just a constant.
Notice that this equation doesn’t contain any variable y. The absence of y means that it can take any values. Here’s an example.
An Example of Graphing a Vertical Line
Graph the vertical line x = 3.
The equation doesn’t have the variable y which implies that it could assume any numerical values for y. In the table of values, you will see that “3” is the repeating value in the column of x while having different values in the column of y.
This is precisely the interpretation of the equation x = 3.
So, we can now plot the points on the xy axis to see how it looks. As you can see, it is a vertical line parallel to the y-axis and passing through the point (3, 0).
On the other hand, the equation of any horizontal lines come in the form
where “c” is just a constant.
This time around, the equation doesn’t have any variable x. The absence of x means that the variable x can take any numerical values while the value of y is being held constant. Here’s an example.
An Example of Graphing a Horizontal Line
Graph the horizontal line y = –2.
Since we have no x-variable in the equation, it is okay to pair the y-coordinate of “-2” with any x-values. When you construct the table of values for this, the y-coordinates will be the same throughout while the x-coordinates will assume different unique values.
Observe, the y-column is populated with the same value of -2.
Graphing these points in the xy axis, we have a horizontal line parallel to the x-axis and passing through the point (0, –2).