If either vector then But the converse need not be true. Justify your answer with an example.

If and then what can be concluded about the vector

If are unit vectors such that find the value of

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 ].

Show that the points A(1, 2, 7), B(2, 6, 3) and C(3, 10, –1) are collinear.