A coordinate system is a set of one, two, three or more coordinate axes. An axis and a unit segment form a coordinate axis. These axes cross in the point of origin. A coordinate system with perpendicular axes is called a perpendicular coordinate system. If such system has the same unit segment for each of the axes then it is called Cartesian coordinate system.
An axis OX is called the abscissa axis, an axis OY is called the ordinate axis.
To define coordinates of point A in a two-dimensional Cartesian coordinate system draw lines perpendicularly to the axes. A pair of distances from the point of origin to the cross points on an abscissa and ordinate axes are the coordinates of the point. The coordinate is positive if the cross point is on the positive half-line of the axis and negative otherwise.
Note that the order of coordinates is important. A point A with coordinates (-3; 2) differs from a point B (2; -3).
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