A and B but not in the ray with initial point A determined by B, will determine another ray with initial point A. With respect to the AB ray, the AD ray is called the opposite ray. Thus, we would say that two different points, A and B, define a line and a decomposition of this line into the disjoint union of an open segment and two rays, BC and AD (the point D is not drawn in the diagram, but is to the left of A on the line AB). These are not opposite rays since they have different initial points. In Euclidean geometry two rays with a common endpoint form an angle. The definition of a ray depends upon the notion of betweenness for points on a line. It follows that rays exist only for geometries for which this notion exists, typically Euclidean geometry or affine geometry over an ordered field. On the other hand, rays do not exist in projective geometry nor in a geometry over a non-ordered field, like the complex numbers or any finite field. Line segment A line segment is a part of a line that is bounded by two distinct end points and contains every point on the line between its end points. Depending on how the line segment is defined, either of the two end points may or may not be part of the line segment. Two or more line segments may have some of the same relationships as lines, such as being parallel, intersecting, or skew, but unlike lines they may be none of these, if they are coplanar and either do not intersect or are collinear. Number line A point on number line corresponds to a real number and vice versa. Usually, integers are evenly spaced on the line, with positive numbers are on the right, negative numbers on the left. As an extension to the concept, an imaginary line representing imaginary numbers can be drawn perpendicular to the number line at zero. The two lines forms the complex plane, a geometrical representation of the set of complex numbers. In graphics design See also Affine transformation Curve Distance between two parallel lines Distance from a point to a line Imaginary line (mathematics) Incidence (geometry) Line segment Generalised circle Locus Plane (geometry) Polyline References External links Equations of the Straight Line at Cut-the-Knot Elementary geometry Analytic geometry Mathematical concepts Infinity