Special Lines 1. Let's look at how to find the slope of a horizontal line. A horizontal line travels to the right, passing through points A and B. Between A and B the run is 8, but the line doesn't rise, so the rise is 0. This makes the slope 0, as shown in the calculation above. A horizontal line has slope 0. 2. Let's look at how to find the slope of a vertical line. A vertical line moves upwards, passing through points A and B. Between A and B the run is 0, and the rise is 5. This means there is no slope, because division by zero is impossible. Note that the slope is NOT zero. There is no slope. To be reminded why this is so, visit our 'dividing by zero' page. A vertical line has NO slope. Summary: Horizontal lines have slope 0.    Vertical lines have no slope. Vertical lines are also not functions. The next step is to look at lines and slope on a set of X-Y axes Introduction | Slope | Special Lines | XY Axes | Intercepts | Quick Graphing Linear Equations | Parallel and Perpendicular | Equation Forms | Finding Equations Resources Content, HTML, graphics & design by Bill Willis 2023