ABSTRACT
A vector is a directed line segment, with two vectors being equal if they have the same length and the same direction. More precisely, a vector is an equivalence class of directed line segments, where two directed segments are equivalent if they have the same length and the same direction. The length of a vector is the common length of its directed segments, and the angle between vectors is the angle between any of their segments. To distinguish them from vectors, the real numbers are called scalars. Associated with each point in space is the vector determined by the directed segment from the origin to that point.
