Using Two Points to Find Slope Page 5 of 5
Undefined SlopeA vertical line that goes straight up and down has an undefined slope. With a vertical line, the run will be 0 because the xvalues are not changing. If you use two points on a vertical line and plug them into the formula for slope, you're going to end up with a 0 in the denominator of the fraction. Since you can't divide by 0, we say that the slope is undefined. Think of the word NO to help you remember: Example 

Find the slope of the line through the points (3,1) and (3,2).
Step 1: Label the points.
Step 1: Label the points.
Step 2: Plug the values into the formula for slope.
Step 3: Make sure the slope is a simplified fraction. There's a problem here! You can't have a 0 in the denominator of a fraction. This means the slope is undefined.
Practice
Ready to try using the formula for slope on your own? Click the START button below to take a practice quiz.

Don't miss the lesson on slopeintercept form!