A vector has both magnitude as well as direction.

Position vectors of any point in space are usually calculated from the origin, so we write three points A ,B,C in space to represent the origin as the initial point.

the angles are called direction angles, which the position vector makes with the positive x-axis ,y-axis and z-axis respectively

Cosines of the angles α,β,γ are called direction cosines.

If l , m and n are the direction cosines of vector denoted by , then , the coordinates of point P are given by : lr ,mr and nr respectively.

A vector whose initial and terminal points coincides is called Zero Vector. The magnitude of Zero Vector is also Zero.

The vector whose magnitude is always 1 or unity is called a Unit Vector.

, is called the unit vector of a given vector in the direction of

Two vectors whose initial point is same are called co- initial vectors.

Two vectors A and B are said to be collinear , if they are parallel to the same line irrespective of their magnitudes and directions.