Introduction to Geometry: Measuring Segments

The Number Line

Our best example of a line is the number line. The midpoint of the number line is called the origin and corresponds to zero. The positive numbers are located to the right of zero and the negative numbers are located to the left of zero.

As you see in the figure below, integers are designated to the points that are equidistant. So, the distance between each two adjacent points is one unit.

number line with the points negative 3, negative 2, negative 1, 0, 1, 2, and 3 labeled

We know that any non-integer number is between two consecutive integers. For example, 2.35 is between 2 and 3 or -3.15 is between -3 and -4. Thus, all rational numbers can correspond to points on a number line. For example, the locations of the numbers -1.70 and 3.20 are points A and B in the number line below:

number line with the points negative 4, negative 3, negative 2, negative 1, 0, 1, 2, 3 and 4 labeled, between negative 2 and negative 1, the point negative 1.70 is labeled and between 3 and 4, the point 3.20 is labeled