Q23 of 52 Page 1

If the points A(x, y), B(3, 6) and C(–3, 4) are collinear, show that x – 3y + 15 = 0.

Point A (x, y)


B (3, 6)


C (-3, 4) are collinear


Collinear means they lie on the same straight line and the Slope of AB = Slope of BC,




y - 6 = 1/3 (x - 3)
y - 6 = 1/3x -1
y - 5 - 1/3x = 0


Multiply by -3,


We get;
-3y + 15 + x = 0


By Re-arranging


We get;
x - 3y + 15 = 0 (proved)


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