1.1.1 Sets of Numbers (continued)
Example 2 Interval Notation
There are many ways to represent sets, such as with words, number lines, inequalities, or by using interval notation. Interval notation can be used to represent the set of all real numbers between two endpoints, called an interval. In interval notation, the symbols [ and ] are used to include an endpoint in an interval, and the symbols ( and ) are used to exclude an endpoint from an interval. An interval that extends forever in the positive direction goes to infinity ( ∞ ), and an interval that extends forever in the negative direction goes to negative infinity ( −∞ ). Because ∞ and −∞ are not numbers, they cannot be included in a set of numbers, so parentheses are used to enclose them in an interval.
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