In mathematics, a number line is a picture of a straight line in which 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. 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, 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 number lines on paper, chalkboard, or screen do not.
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
. The real numbers consist of 
