The size (or length) of the vector AB (with → on AB) is called the module of the vector, and it is denoted as | AB | (with → on AB) or | a |.

computing formula

Space vector (x, y, z), where x, y and z are the coordinates on three axes respectively, and the module length is: under the radical sign (x 2+y 2+z 2). Where x 2 represents the square of x, the plane vector (x, y), and the module length under the radical sign is: (x 2+y 2) belongs to the n-dimensional complex vector space x=(x 1, x2 ..., xn) x, and the module is ‖x‖=sqrt((x