## Intermediate Algebra for College Students (7th Edition)

RECALL: $\text{slope} = \frac{\text{change in y}}{\text{change in x}}$ The points on a vertical line share the same x-value. This means that for any two given points, the change in x-value is 0. Since the denominator of $\frac{\text{change in y}}{\text{change in x}}$ is 0, for whatever value of the numerator, the slope will always be undefined (division of zero is not allowed). Thus, the slope of a vertical line is undefined.