Line (geometry).

Line (geometry). Line (geometry), a series of adjacent points that extends to infinity in two directions. Although the word line can be used to refer to any stroke on paper, a line is usually considered to be straight, meaning that all of its points lie in a row. The edge of a ruler, infinitely extended, is a good approximation of a line. Lines are onedimensional--they have length but no width or depth. Two points are sufficient to define a line because one and only one line may be drawn through any pair of points. Lines are often named for the points through which they pass; a line passing through point A and point B may be denoted . Lines may be represented in two dimensions by equations of the general form y = mx + c, where m is the slope of the line and c is a constant that determines where the line crosses the y-axis. Every point that lies on the line must satisfy the equation. For example, we can prove that the point (2,6) lies on the line y = 3x by substituting 2 for x and 6 for y in the line's equation: 6 = 3(2). The slope of this line is m = 3. See also Line segment; Ray. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.