Question

Given mc012-1.jpg, what is the equation of the line that passes through the points (–p, –q) and (p, q)?
y = –x
mc012-2.jpg
y = q
y = 2x + (2p – q)

Answer 1

Slope = (q - (−q)) / (p - (−p)) = 2q / 2p = q/p.
Point-slope: y - q = (q/p)(x - p) ⇒ y = (q/p)x.

(If p = 0 the two points are (0,−q) and (0,q) and the line is x = 0.)