Intervals
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Interval is a set of real numbers, which are greater than (or equal to) a given number (or negative infinity) and at the same time, less than (or equal to) another number (or infinity).
Types of intervals:
Finite interval is limited from both sides by given values, e.g. (-3,2].
Interval infinite is limited at most from one side, e.g. (2, \infty) or (-\infty, \infty).
Graphing on a real number line:
Filled-in circle on a real number line or a square bracket in the interval notation indicates that the endpoint is part of the stated interval.
Open circle on a real number line or a round bracket in the interval notation indicates that the endpoint doesn't belong to the stated interval.
Through a union of intervals, a new interval will be created containing numbers, which are at least in one of them.
Intersection of intervals is a new interval, which contains numbers that all intervals have in common.