There are two ways to approach this.
Option #1:
Use the slope formula [tex]m = \dfrac{y_2-y_1}{x_2-x_1}[/tex].
[tex]m= \dfrac{6-(-5)}{11-11} = \dfrac{11}{0}[/tex]
That value is undefined, so the slope is undefined.
Option #2:
Because the two points have the same x-value, they will be vertically above/below one another. This means your line is a vertical line and the slope of a vertical line is undefined.
Either way, your slope is undefined.
