1. vector does not consider the endpoint, and vector translation does not change the vector, so any two vectors can move to a point. The projection from a vector to b vector refers to the modulus of a vector multiplied by the cosine of the angle between a vector and b vector. The projection of B vector to A vector refers to the modulus of B vector multiplied by the cosine of the included angle between A vector and B vector.

Let the angle between two non-zero vectors A and B be θ, then (∣ b ∣ cos θ) is called the projection of vector B in the direction of vector A. According to the definition, the projection of one vector in the direction of another vector is a quantity. When θ is an acute angle, it is a positive value. 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∣.