Unbounded Intervals

Intervals which expands indefinitely in both the directions are known as unbounded intervals.
1. (a,infinity) is the set of all real numbers x such that a < x.
2. (–infinity, a) is the set of all real numbers x such that x < a.
3. [a, +infinity) is the set of all real numbers x such that a <= x.
4. (–infinity, a] is the set of all real numbers x such that x <= a.