When the **0** is on the "**top**" of the fraction, that would mean that the two y-values are the same. Thus that line is horizontal (**slope** of **0**). **If** the "bottom" of the fraction is **0** that means the two x-values are the same. Thus that line is vertical (undefined **slope**).

What do you do if the slope is 0?

Since we did not have a change in the x values, the denominator of our **slope** became **0**. This means that we have an undefined **slope**. If you were to graph the line, it would be a vertical line, as shown above. This form can be handy if you need to find the **slope** of a line given the equation.

When the slope is 0 What does that mean?

Now we see why a vertical line has an undefined **slope**. Because we can't divide by zero! Usually in math, when something is "undefined" **it means** that somewhere, something is being divided by **0**. And that's a no-no. It has no **meaning**.

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