( x) Coplanar Vectors A system of vectors is said to be coplanar, if their supports are parallel to the same plane. Otherwise they are called noncoplanar vectors.
( xi) Reciprocal of a Vector A vector having the same direction as that of a given vector but magnitude equal to the reciprocal of the given vector is known as the reciprocal of a.
i. e., if | a | = a, then | a-1 | = 1 / a.
Addition of Vectors
Let a and b be any two vectors. From the terminal point of a, vector b is drawn. Then, the vector from the initial point O of a to the terminal point B of b is called the sum of vectors a and b and is denoted bya + b. This is called the triangle law of addition of vectors.
Parallelogram Law
Let a and b be any two vectors. From the initial point of a, vector b is drawn and parallelogram OACB is completed with OA and OB as adjacent sides. The vector OC is defined as the sum of a and b. This is called the parallelogram law of addition of vectors.
The sum of two vectors is also called their resultant and the process of addition as composition.