- The open interval a<x<ba<x<ba<x<bis identified by the notation (a,b)(a, b)(a,b). We write x∈(a,b)x \in (a, b)x∈(a,b)
- The closed interval a≥x≥ba\geq x\geq ba≥x≥b is identified by the notation [a,b][a, b][a,b]. We write x∈[a,b]x \in [a, b]x∈[a,b]
- We can also have half-open intervals (to the left, to the right)
- All of the above are bounded intervals. An interval that goes to positive or negativ