*Macmillan Science Library: Mathematics*. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.

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## The Cartesian Coordinate System

Cartesian coordinates are used to locate a point in space by giving its relative distance from **perpendicular** intersecting lines. In coordinate geometry, all points, lines, and figures are drawn in a **coordinate plane**. By reference to the two coordinate axes, any point, line, or figure may be precisely located.

In Descartes's system, the first coordinate value (*x*-coordinate) describes where along the horizontal axis (the *x*-axis) the point is located. The second coordinate value (*y*-coordinate) locates the point in terms of the vertical axis (the *y*-axis). A point with coordinates (4, -2) is located four units to the right of the intersection point of the two axes (point O, or the origin) and then two units below the vertical position of the origin. In example (a) of the figure, point D is at the coordinate location (4, -2). The coordinates...

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