Figure 5.5 illustrates the four types of relations that describe inequalities. The relationships that characterize inequalities can unfold in inclusive and exclusive (or non-inclusive) ways. When you use a number line, representing inclusion or exclusion involves two basic activities:
A range of numbers can be greater than a given value on a number line. To show that the range of numbers is greater than a given number, you employ an open circle. The circle excludes the circled number from the range.
A range of numbers can be greater than or equal to a given value on a number line. To show that the number is included in the range, you use a filled circle.