CEVAP:

Intervals are important subsets of the real numbers. Given two real numbers a and b with a < b the set {x| x ? R and a ? x ? b}is called a closed interval and is denoted by [a, b]. Similarly, the half-open intervals (a, b], [a, b) are defined as (a, b] = {x| x ? R and a < x ? b}, [a, b) = {x| x ? R and a ? x < b}.The intervals, defined above are finite intervals. Using the symbols ? (plus infinity) and –? (minus infinity) unbounded intervals can be defined, namely

(a, ?) = {x| x ? R and x > a},

a, ?) = {x| x ? R and x ? a},

(–?, b) = {x| x ? R and x < b},
(–?, b] = {x| x ? R and x ? b}.