number line

A number line, invented by John Wallis, is a one-dimensional picture in which the integers are shown as specially-marked points evenly spaced on a line. Although this image only shows the integers from -9 to 9, the line includes all real numbers, continuing "forever" in each direction. It is often used as an aid in teaching simple addition, subtraction, especially involving negative numbers.

It is divided into two symmetric halves by the origin, i.e. the number zero.

Drawing the number line

The number line is most often represented as being horizontal. Customarily, positive numbers lie on the right side of zero, and negative numbers lie on the left side of zero. An arrow on either end of the drawing is meant to suggest that the line continues indefinitely in the positive and negative directions, even though ones paper, chalkboard, or screen does not.

The set of all numbers on the number line is otherwise known as the set of the reals, denoted by R. The real numbers consist of irrational and rational numbers, as well as integers, whole numbers, and the natural numbers (the counting numbers).

A line drawn through the origin at right angles to the real number line can be used to represent the imaginary numbers. This extends the number line to a number plane, with points on the plane representing complex numbers.

See also

• Real number
• Extended real number line
• Number form (neurological phenomenon)
• Timeline

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