Elementary Algebra

$m=\dfrac{b-d}{a-c}$
Using $m=\dfrac{y_1-y_2}{x_1-x_2}$, the slope of the line determined by the given points, $( a,b ) \text{ and } ( c,d ),$ is \begin{array}{l}\require{cancel} m=\dfrac{b-d}{a-c} .\end{array}