Max, Min, Sup, Inf - Purdue University

Each of the numbers 1.4, 1.41, 1.414, 1.4142, etc. is rational and has square less than 2. Their limit is √ 2. Thus, supS = √ 2. (See Exercise 6 below.) Since √ 2 is irrational, S is then an example of a set of rational numbers whose sup is irrational. Suppose, however, that we (like the early Greek mathematicians) only knew about ...

  Rational, Irrational, Is irrational