DIAGRAM

(in geom.), a figure consisting of points, lines, and curves drawn for the purpose of helping a reader to follow the argument used in demonstrating a geometrical proposition. Points are named by letters of the alphabet: A, B, etc. In the text, a line is referred to by the two letters naming the points which it joins: line, ete.,, and an angle by three letters, the middle one of which is always the name of the point of juncvion of the two lines forming the angle: angle ABC, or CBA.