Namely: prjba = | a | * cos < a, b >；; =a b/|b| .
Mathematically, a geometric vector (also called Euclidean vector, usually abbreviated as vector, abbreviated as vector) refers to a geometric object with size and direction, which can be visualized as a line segment with an arrow: the arrow indicates the direction of the vector, the length of the line segment and the size of the vector.
Extended data:
Vector notation: print letters (such as A, B, U, V) in bold, and add a small arrow "→" at the top of the letter when writing. If the starting point (a) and the ending point (b) of the vector are given, the vector can be recorded as AB (and added to the top →). In the space Cartesian coordinate system, vectors can also be expressed in pairs. For example, (2,3) in the xOy plane is a vector.
In physics and engineering, geometric vectors are more often called vectors. Many physical quantities are vectors, such as the displacement of an object, the force exerted on it by a ball hitting a wall and so on. On the contrary, it is scalar, that is, a quantity with only size and no direction. Some definitions related to vectors are also closely related to physical concepts. For example, vector potential corresponds to potential energy in physics.
Baidu Encyclopedia-Vector