To locate an object or a point on a plane, called the Cartesian (or coordinate) plane, two perpendicular lines are required. These lines are called the coordinate axes. The horizontal line is called the x - axis, and the vertical line is called the y - axis.
The coordinate axes divide the plane into four parts called quadrants. The point of intersection of the axes is called the origin. The distance of a point from the y - axis is called its x-coordinate, or abscissa, and the distance of the point from the x-axis is called its y-coordinate, or ordinate. If the abscissa of a point is x and the ordinate is y, then (x, y) are called the coordinates of the point. The coordinates of a point on the x-axis are of the form (x, 0) and that of the point on the y-axis are (0, y). The coordinates of the origin are (0, 0).
The coordinates of a point in the first quadrant are of the form (+ , +), (–, +) in the second quadrant, (–, –) in the third quadrant and (+, –) in the fourth quadrant, where + denotes a positive real number and – denotes a negative real number.