Question
If A (2, – 1, 3), B (8, 5, – 6) and C (4, 1, 0) are the vertices of a triangle. show that
(i) AB = 3 AC
(ii) The direction-cosines of 
are 
Solution
Let O be the origin.
A is (2, -1, 3)
B is (8, 5, -6)
C is (4, 1, 0)
(i)
(ii)
direction cosines of 
i.e., coeffs. of 
are 
A is (2, -1, 3)
B is (8, 5, -6)
C is (4, 1, 0)
(i)
(ii)
direction cosines of i.e., coeffs. of are 
