## Precalculus (6th Edition)

A parenthesis will be used when the number that serves as a boundary (either lower or upper boundary) is not included in the set. A square bracket will be used when the number that serves as a boundary (either lower or upper boundary) is included in the set. Examples: (1) $(3, 9)$ means 3 and 9 are not included in the set (2) $(3, 9]$ means 3 is not included but 9 is included in the set (3) $[3, 9]$ means both 3 and 9 are included in the set