, The number plane, or Cartesian plane, is divided into four quadrants by two perpendicular lines called the x-axis, a horizontal line, and the y-axis, a vertical line. These axes intersect at a point called the origin. Once a unit distance has been chosen, the position of any point in the plane can be uniquely represented by an ordered pair of numbers (x,y). For the point (5,3), for example, 5 is the x-coordinate and 3 is the y-coordinate, sometimes called the first and second coordinates. When developing trigonometry, the four quadrants are usually called the first, second, third and fourth quadrants as shown in the following diagram.
