WAEC 2020 · Paper 1 · Q36

$P(3, 4)$ and $Q(-3, -4)$ are two points in a plane. Find the gradient of the line that is normal to the line $PQ$ .

Worked solution (try it first)

Gradient of $PQ$ : $\dfrac{-4 - 4}{-3 - 3} = \dfrac{-8}{-6}$
$= \dfrac{4}{3}$ .
A normal is perpendicular, so its gradient is the negative reciprocal: $-\dfrac{1}{4/3} = -\dfrac{3}{4}$ .
So the gradient of the normal is $-\frac{3}{4}$ , option C.