Let a and b be fixed real numbers such that a < b on a number line. The different types of intervals we have are
The open interval (a, b): We define an open interval (a, b) with end points a and b as a set of all real numbers "x", such that a < x < b. That is, the real number x will be taking all the values between a and b. An important point to consider in this case is the type of brackets used. Generally open intervals are denoted by ordinary brackets ( ). The closed interval [a, b]: We define a closed interval [a, b] with end points a and b as a set of all real numbers "x", such that a ≤ x ≤ b. In this case the real number x will be taking all the values between a and b inclusive of the end points a and b. Generally closed intervals are denoted by [ ] brackets. The half open interval [a, b): We define a half open interval [a, b) with end points a and b as a set of all real numbers "x", such that a ≤ x < b. In this case the real number x will be taking all the values between a and b, inclusive of only a but not b. The half open interval (a, b]: We define a half open interval (a, b] with end points a and b as a set of all real numbers "x", such that a < x ≤ b. In this case the real number x will be taking all the values between a and b, inclusive of only b but not a.
The open interval (a, b): We define an open interval (a, b) with end points a and b as a set of all real numbers "x", such that a < x < b. That is, the real number x will be taking all the values between a and b. An important point to consider in this case is the type of brackets used. Generally open intervals are denoted by ordinary brackets ( ).
The closed interval [a, b]: We define a closed interval [a, b] with end points a and b as a set of all real numbers "x", such that a ≤ x ≤ b. In this case the real number x will be taking all the values between a and b inclusive of the end points a and b. Generally closed intervals are denoted by [ ] brackets.
The half open interval [a, b): We define a half open interval [a, b) with end points a and b as a set of all real numbers "x", such that a ≤ x < b. In this case the real number x will be taking all the values between a and b, inclusive of only a but not b.
The half open interval (a, b]: We define a half open interval (a, b] with end points a and b as a set of all real numbers "x", such that a < x ≤ b. In this case the real number x will be taking all the values between a and b, inclusive of only b but not a.