The Real Number Line. The most intuitive way is to use the real number line . A bigger number will always be found to the right of a smaller number. We visualize a set on the real number line by marking its members. The following graph depicts all real numbers which are either greater than 2 or strictly between -1 and 1.
Interval notation translates the information from the real number line into symbols.
Our example is written in interval notation as . Therefore we always exclude them as endpoints by using parentheses. An interval is called closed , if it contains its endpoints, such as . The whole real line is considered to be both open and closed. Sets are delimited by curly braces.