Persamaan garis lurus yang melalui titik (2,1) dan (-2,-7) adalah

Y-y1/y2-y1 = x-x1/x2-x1

(y-1)/(-7-1)=(x-2)/(-2-2)

(y-1)/-8 = (x-2)/-4

-4(y-1)=-8(x-2)
(y-1)=2(x-2)
y-1=2x-4
y=2x-3

(y-1)(-2-2) = (x-1)(-7-1)
(y-1)(-4) = (x-2)(-8)
-4y + 4 = -8x + 16
-4y + 8x + 4 – 16 = 0
8x – 4y – 12 = 0
2x – y – 3 = 0