## Intermediate Algebra (12th Edition)

$m=-\dfrac{1}{3}$
Using the properties of equality, the given equation, $3x-y=4$ is equivalent to \begin{array}{l}\require{cancel} -y=-3x+4 \\\\ y=3x-4 .\end{array} Using $y=mx+b$ where $m$ is the slope, then the slope, $m$, of the equation above is \begin{array}{l}\require{cancel} m=3 .\end{array} Since perpendicular lines have negative-reciprocal slopes, then a line perpendicular to the equation above will have $m=-\dfrac{1}{3} .$