Decomposition of a vector in a plane
Theorem
If and be any two non-zero and non-collinear vectors then any vector in the plane of and can be uniquely expressed as the sum of two vectors parallel to the vectors and .
Proof: Let and be any two non-zero and non-collinear plane vectors. Let be any other vector in the plane of the vectors and . Now from the point P draw the straight lines PG and PH parallel to the lines OA and OB as shown in the succeeding figure below.