To find the slope of a line that passes through two points you have to use the following formula
[tex]m=\frac{y_1-y_2}{x_1-x_2}[/tex]Where
(x₁,y₁) are the coordinates of one of the points
(x₂,y₂) are the coordinates of the other point
The points (17,-13) and (17,8) have the same x-coordinate, x=17, if you replace the coordinates on the formula you will see that the denominator of the division is equal to zero. This means that the slope is undefined:
[tex]\begin{gathered} m=\frac{8-(-13)}{17-17} \\ m=\frac{8+13}{0} \end{gathered}[/tex]An undefined or infinite slope indicates that no matter what the value of y is, the value of x will remain the same. This is an example of a vertical line.
