Gradien garis yang melalui titik p(-5,1) dan q(2,-8) adalah

gradien = y2 - y1 / x2 - x1
  = (-8 - 1) / (2 - (-5))
  = -9 / 7

(y-y1)/(y2-y1) = (x-x1)/(x2-x1)
(y-1)/(-8-1) = (x+5)/(2+5)
7y - 7 = -9x - 45
7y = -9x - 38
y = -9x/7 + 38/7

gradiennya
= -9/7