Let A (2, 3, 4), B (- 1, - 2, 1), C (5, 8, 7) be given
Direction ratio of AB are (- 1 - 2), (- 2 - 3) (1 - 4) = (-3,-5,-3)
Direction r ratio of AC are (5 - 2), (8 - 3), (7 - 4) = (3, 5,3)
The direction ratios of AB and AC are proportional.
So AB and AC are parallel
But A is common in AB and AC
A, B and C are collinear.
