In this section, we will graph equations with only one variable. That is, there is just x and no y, or just y without an x. A vertical line is the graph of an equation that can be written in the form ...In this section, we will graph equations with only one variable. That is, there is just x and no y, or just y without an x. A vertical line is the graph of an equation that can be written in the form x = a. The line passes through the x -axis at (a, 0). A horizontal line is the graph of an equation that can be written in the form y = b. The line passes through the y-axis at (0, b).