Geometry Practice Test 6

12x + 3y = 15
y = −4x + 5 ......(i)
$\frac{\mathit{x}}{2}-2\mathit{y}$ = $\frac{19}{2}$
y = $\frac{4\mathit{x}}{4}-19$ ... (ii)
In both lines (i) and (ii),
Slope = -4 and $\frac{1}{4}$ respectively
Product = - 4 × $\frac{1}{4}$ = - 1
Product of slopes is -1. Hence, they are perpendicular.