If the vertices A, B, C of a triangle ABC are (1, 2, 3), (–1, 0, 0), (0, 1, 2),
respectively, then find ∠ABC [∠ABC is the angle between the vectors BA
uuur
and BC
uuur ] 16 Show that the points A(1, 2, 7), B(2, 6, 3) and C(3, 10, –1) are collinear