As distinct from the rectangular system, the angles between the coordinate axes need not be straight angles. They subdivide the space into eight regions, the octants.Ī skew-angled (general) Cartesian coordinate system is also occasionally used. The plane passing through the coordinate axes are said to be the coordinate planes. The rectangular Cartesian coordinates of a point $M$ are represented by an ordered pair of numbers $(x,y)$, the first of which (the abscissa) is equal to the magnitude of the orthogonal projection of the directed segment $0M$ on the abscissa axis, the second one (the ordinate) being the orthogonal projection of the directed segment $0M$ on the ordinate axis.Ī Cartesian rectangular coordinate system in a three-dimensional space is defined similarly to the case of the plane: by an abscissa axis, by an ordinate axis, by an applicate axis, and by a coordinate origin $0$. The coordinate axes subdivide the plane into four equal regions, called quarters or quadrants. One of the coordinate axes $(0x)$ is said to be the abscissa axis the other one ($0y$) is said to be the ordinate axis. The point of intersection ($0$) of the coordinate axes is said to be the coordinate origin. On a plane, a Cartesian rectangular coordinate system is defined by two mutually-perpendicular lines, the coordinate axes, on each of which a positive direction has been chosen and a segment of unit length has been specified. A rectilinear system of coordinates in a Euclidean space.

History of abscissa