Chapter 2 - Summary Exercises - Finding Slopes and Equations of Lines - Page 178: 2

$m=0$

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