# How to Graph Vertical and Horizontal Lines

The equation of a 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 $\left( {3,0} \right)$.

On the other hand, the equation of a horizontal line comes 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 can have different 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 $\left( {0, - 2} \right)$.