Show that if A is an infinite set, then it contains a countably infinite subset.

SolutionStep 1In this problem, we have to prove that if A is infinite sets then it contains a countable infinite subset.Let us assume that A is infinite sets of countable sets. Let the element of the set A be a1, a2, a3, ……….an. Now consider that a1 A then a1 is not an empty set or null sets.Another case consider that {a1, a2} A then a1 and a2 is not an empty sets.