The Rectangular Coordinate Plane (1)

Recall the concept of a number line. Every point on a number line is associated with exactly one real number and every real number is associated with exactly one point on the number line. This is the same as saying there is a one-to-one correspondence between the set of points on the number line and the set of real numbers.

The rectangular coordinate plane is an extension of the concept of a number line. Instead of a line, however, you need to consider a plane. There is also a one-to-one correspondence between the set of all points on the rectangular coordinate plane and the set of all ordered pairs of real numbers. Below is an illustration of a rectangular coordinate plane.

Look at the horizontal and vertical number lines in the figure. These are called the x-axis and the y-axis, respectively. Notice the arrow that points to the right on the x-axis and the other arrow that points upward on the y-axis. These arrows indicate the positive direction on each number line. The arrow that points to the left of the x-axis and the arrow that points downward on the y-axis indicate the negative direction on each number line.