Exercise 21.
Find an example of sets \(A\) and \(B\) such that \(|A| = 3\text{,}\) \(|B| = 4\text{,}\) and \(|A \cup B| = 5\text{.}\)
Find an example of sets \(A\) and \(B\) such that \(|A| = 3\text{,}\) \(|B| = 4\text{,}\) and \(|A \cup B| = 5\text{.}\)