Chapter 3 - Introduction to Graphing - 3.5 Slope - 3.5 Exercise Set - Page 200: 48

$m=-2$

Using $m=\dfrac{y_1-y_2}{x_1-x_2}$ or the Slope Formula, then the slope of the line containing the given points, $\left( -1,4 \right) \text{ and } \left( 5,-8 \right)$, is \begin{array}{l} m=\dfrac{4-(-8)}{-1-5} \\\\ m=\dfrac{4+8}{-1-5} \\\\ m=\dfrac{12}{-6} \\\\ m=-2 .\end{array}