## Algebra: A Combined Approach (4th Edition)

$5x + 10y = -7$ $5x + 10y = 0$
$5x + 10y = -7$ $5x + 10y = 0$ They are perpendicular to $10x - 5y = -7$ because they have a slope of $m_{perpendicular}=-\frac{5}{10}=-\frac{1}{2}$, which is the negative reciprocal of the slope of $10x - 5y = -7$ ($m=2$)