A value that represents a quantity along a continuous line is defined as a real number. The set of all real numbers is usually denoted by ‘R’.
A straight line on which real numbers can be pictured as points is called a real number line, or simply a number line.
To construct a real number line, we draw a straight line and label any convenient point with the number '0', called the origin.
Now we choose any convenient length and use it to locate other points.
Points to the right of '0' correspond to the positive real numbers and points to the left of '0' correspond to the negative real numbers.
The point on a real number line that corresponds to a real number is called the graph of the number. Drawing the point is called graphing the number or plotting the point.
The number that corresponds to a point on a real number line is called the co-ordinate of the point.
The numbers on a number line increase from left to right. When graphing two numbers on a number line, the number to the right is always greater.