Calculus I > Precalculus Review

Intervals

An interval is a set of real numbers “between two endpoints,” say $ a$ and $ b$. Depending on whether it includes endpoints or not, and whether it is finite or infinite, the following types of an interval are considered.

Finite interval Notation
$ a < x < b$ $ (a,\: b)$
$ a \le x \le b$ $ [a,\: b]$
$ a \le x < b$ $ [a,\: b)$
$ a < x \le b$ $ (a,\: b]$

Infinite interval Notation
$ x > a$ $ (a,\: \infty)$
$ x \ge a$ $ [a,\: \infty)$
$ x < b$ $ (-\infty,\: b)$
$ x \le b$ $ (-\infty,\: b]$

The set of all real numbers can be viewed as a special case of interval, denoted by  $ (-\infty, \infty)$.


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