If and are two vectors such that then prove that vector is perpendicular to the vector

Three vertices of a triangle are A(0, - 1, - 2), B(3, 1, 4) and C(5, 7, 1). Show that it is a right - angled triangle. Also, find its other two angles.

If the position vectors of the vertices
A, B and C of a ∆ABC be (1, 2, 3), ( - 1, 0, 0) and (0, 1, 2) respectively then find ∠ABC.

If and are two unit vectors such that find

If and then express in the form where and