Question

Find the least upper bound (if it exists) and the greatest lower bound (if it exists) for the given set.
[5,7]

Answer 1

S=[5,7].
The set of upper bound elements is the set of numbers which
are greater than or equal to every element of S.
So, it is [7, +inf) and the
least element is 7.
The set of lower bound elements is the set of numbers
which are less than or equal to every element of S.
So, it is (-inf, 5] and
the greatest element is 5.
So, Sup(S) = 7 and Inf(S) = 5.