Ordered pairs are always written with x first and then y, (x,y). Second, from the point on the x-axis given by the first number count up or down the number of spaces designated by the second number of the ordered pair. Points are located on the plane in the following manner.įirst, start at the origin and count left or right the number of spaces designated by the first number of the ordered pair. The ordered pair (5,7) is not the same as the ordered pair (7,5). This is called an ordered pair because the order in which the numbers are written is important. Points on the plane are designated by ordered pairs of numbers written in parentheses with a comma between them, such as (5,7). These are numbered in a counterclockwise direction starting at the upper right. The plane is divided into four parts called quadrants. Thus the plane extends indefinitely in all directions. The arrows indicate the number lines extend indefinitely. Positive is to the right and up negative is to the left and down. The zero point at which they are perpendicular is called the origin. The horizontal line is the x-axis and the vertical is the y-axis. Study the diagram carefully as you note each of the following facts. Perpendicular means that two lines are at right angles to each other. This system is composed of two number lines that are perpendicular at their zero points. This scheme is called the Cartesian coordinate system (for Descartes) and is sometimes referred to as the rectangular coordinate system. Rene Descartes (1596-1650) devised a method of relating points on a plane to algebraic numbers. Note that this concept contains elements from two fields of mathematics, the line from geometry and the numbers from algebra. We have already used the number line on which we have represented numbers as points on a line.
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