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Number line
From Wikipedia, the free encyclopedia
A number line 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 or subtraction, especially involving negative numbers.
It is divided into two symmetric halves by the origin, i.e. the number zero.
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 "forever", even though one's 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).