Answer
$m=\text{undefined}$
Work Step by Step
Using $m=\dfrac{y_1-y_2}{x_1-x_2}$ or the Slope Formula, the slope of the line through $(
-1,5
)$ and $(
-1,-4
)$ is
\begin{array}{l}\require{cancel}
m=\dfrac{5-(-4)}{-1-(-1)}
\\\\
m=\dfrac{5+4}{-1+1}
\\\\
m=\dfrac{9}{0}
\\\\
m=\text{undefined}
.\end{array}
