ordonnées

Ordonnées is the plural form of ordonnée, the French term for the vertical coordinate in a Cartesian coordinate system. An ordered pair (x, y) identifies a point on the plane, where x is the abscisse (the horizontal coordinate) and y is the ordonnée (the vertical coordinate). The ordonnée indicates the point’s position relative to the x-axis: it is positive above the axis and negative below it.

In practice, the ordonnée describes the vertical position of points on graphs. For a function y = f(x), the ordonnée corresponds to the value of the function at the input x, so the graph consists of all points (x, f(x)). Moving upward in the plane increases the ordonnée, while moving downward decreases it.

The concept extends to higher dimensions: a point in three-dimensional space has coordinates (x, y, z), where y is the second coordinate and plays the role of the ordonnée in the two-dimensional sense. Terminology can vary by language, but in French ordonnée is the standard term for the second coordinate.

Historically, the Cartesian coordinate system, which unites algebra and geometry, was introduced by René Descartes. The ordonnée, together with the abscisse, forms the fundamental pair used in Cartesian coordinates to locate points and describe geometric relationships. See also coordonnées cartésiennes, système de coordonnées, abscisse.