In basic mathematics, a number line is a picture
of a straight line on which every point is
assumed to correspond to a real number and
every real number to a point.
Often the integers are shown as specially-marked
points evenly spaced on the line.
Although this image only shows the integers
from −9 to 9, the line includes all real
numbers, continuing forever in each direction,
and also numbers not marked that are between
the integers.
It is often used as an aid in teaching simple
addition and subtraction, especially involving
negative numbers.
It is divided into two symmetric halves by
the origin, that is the number zero.
In advanced mathematics, the expressions real
number line, or real line are typically used
to indicate the above-mentioned concept that
every point on a straight line corresponds
to a single real number, and vice versa.
Drawing the number line
The number line is usually represented as
being horizontal.
Positive numbers always lie on the right side
of zero, and negative numbers always lie on
the left side of zero.
An arrowhead on either end of the drawing
is meant to suggest that the line continues
indefinitely in the positive and negative
real numbers, denoted by . The real numbers
consist of irrational numbers and rational
numbers, as well as the integers, whole numbers,
and the natural numbers.
A line drawn through the origin at right angles
to the real number line can be used to represent
the imaginary numbers.
This line, called imaginary line, extends
the number line to a complex number plane,
with points representing complex numbers.
See also
Coordinate system
Complex plane
Extended real number line
Number form
Line
Real number
Timeline
References
