On the number axis of a graph, all arrays greater than x and less than x+a form an open interval.
2. In elementary algebra, traditionally, interval refers to a set, which includes all real numbers between two specific real numbers, and may also include these two real numbers (or one of them). Interval representation is a way to represent variables in an interval. In general interval representation, brackets indicate exclusion and brackets indicate inclusion. For example, the open interval (10,20) means all real numbers between 10 and 20, but does not include10 or 20. On the other hand, closed intervals represent all real numbers between 10 and 20 and between 10 and 20.
3. The definition of interval can be extended to any subset S of totally ordered set T, so that if both X and Y belong to S, and X
A particularly important case is when T=\mathbb {R} }T = \mathbb{R}.
{\ displaystyle \ mathbb {r}} \ mathbb {r} has the following eleven intervals ({\displaystyle a}a and {\displaystyle b}b are real numbers, while {\displaystyle a}