Answer
$Slope_{perpendicular} = \frac{B}{A}$
Work Step by Step
To find the slope of a line that is perpendicular to another, the result of the slopes' multiplication must be $-1$. Therefore, since the original exercise is $$Ax + By + C = 0$$, we must first identify the slope of this equation by re-writing it into general form: $$By = -Ax - C$$ $$y = -\frac{A}{B}x - \frac{C}{B}$$ where the slope is defined as $m = -\frac{A}{B}$. The slope of the perpendicular line, $m_{perp}$ is, therefore: $$-\frac{A}{B}m_{perp} = -1$$ $$m_{perp} = \frac{B}{A}$$.
