θ is the angle between two vectors.

| b | * cos θ is called the projection of vector b on vector a.

| a | * cos θ is called the projection of vector a on vector B.

Extended data plane vector is a quantity with both direction and size in two-dimensional plane, which is also called vector in physics, as opposed to a quantity (scalar) with only size and no direction. Plane vectors are represented by small arrows above A, B and C, and can also be represented by the first and last letters of vector directed line segments.

Modern vector theory is based on the geometric representation of complex numbers. /kloc-in the 0/8th century, due to the use of complex numbers in some mathematical derivation, the geometric representation of complex numbers has become a hot topic. Hamilton discovered quaternions in the process of making a modular simulator of three-dimensional complex numbers. Subsequently, Gibbs and Harvey created a vector analysis system based on quaternion, which was finally widely accepted.

Reference Plane Vector _ Baidu Encyclopedia