In interval notation, what does a bracket indicate?

In interval notation, a bracket indicates that the endpoints of the interval are included in the set. This is known as a closed interval. For example, if we see [a, b], it means that the interval includes all numbers x such that a ≤ x ≤ b. This signifies that both the lower limit (a) and the upper limit (b) are part of the interval, representing definite limits on the range of values included.

In contrast, parentheses would indicate that the endpoints are not part of the interval, denoting an open interval. Hence, the use of brackets signifies the concept of definite limits rather than indefinite or infinite ones. This makes it clear to which specific values the interval refers, establishing a precise range.