ABSTRACT
M4.1. Points, Segments, and Coordinate Plane M4.1.1. Cartesian and Polar Coordinates on Plane ◮ Rectangular Cartesian coordinates in the plane. A rectangular Cartesian coordinate system consists of two mutually perpendicular directed lines, called coordinate axes, each treated as a number line (see Subsection M6.1.1). The point of intersection of the axes is called the origin and usually labeled with the letter O, while the axes themselves are called the coordinate axes. As a rule, one of the coordinate axes is horizontal, directed from left to right, and called the abscissa axis. The other axis is vertical, directed upwards, and called the ordinate axis. The two axes are usually denoted by X or OX and Y or OY , respectively, and the coordinate system itself is denoted by XY or OXY . The two coordinate axes divide the plane into four parts, which are called quadrants and numbered I, II, III, and IV counterclockwise as shown in Fig. M4.1.
