Vector a Vector b = | a |||| b | * cos θ (θ is the included angle between two vectors).

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

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

Tóuyǐng, a mathematical term, refers to the shadow cast by a figure on a surface or a line.

Let the included angle between two non-zero vectors A and B be θ, then | b | cos θ is called the projection or nominal projection of vector B in the direction of vector A.

By introducing the unit vector a(A) of A into the formula, the vector projection of B on A can be defined.

By definition, the projection of one vector in the direction of another vector is a quantity. When θ is an acute angle, it is positive; When θ is a right angle, it is 0; When θ is an obtuse angle, it is negative; When θ = 0, it is equal to | b | When θ = 180, it is equal to | b |.