No matter what the change in x along the line, the slope must always equal zero. Therefore, the change in x along the line is zero. Zero divided by any number is zero. Horizontal lines have a slope of 0. Since we cannot divide by zero, we say the slope of a vertical line is infinite.
Vertical lines have an infinite slope.
You are now ready to try a practice problem. If you have already completed the first practice problem for this unit you may wish to try the additional practice.