Exercise · ZW-INFINITE-SET-007 · ★★☆ Intermediate
Let \(A\) be finite and \(B\) infinite. What can be said about \(A\cup B\)?
Choose one option.
Show answer
- D. It is infinite
Explanation
\(A\cup B\) contains \(B\), which is infinite, so \(A\cup B\) is infinite whatever \(A\) is.
Review the concept: Infinite set
A set \(A\) is infinite if it is not finite, that is, if there is no bijection between \(A\) and \(\{1,\dots,n\}\) for any \(n\in\mathbb{N}\).
\[A\not\sim\{1,\dots,n\}\ \ \forall n\in\mathbb{N}\]
More practice problems: infinite set
- ZW-INFINITE-SET-001 How is an infinite set defined?
- ZW-INFINITE-SET-002 Which of these sets is infinite?
- ZW-INFINITE-SET-003 If A⊆ B and A is infinite, what follows about B?
- ZW-INFINITE-SET-004 Can an infinite set be a subset of a finite set?
- ZW-INFINITE-SET-005 Is [0,1] a finite set?
- ZW-INFINITE-SET-006 If A is infinite, is there a bijection between A and \1,dots,n\ for some n∈ℕ?
- ZW-INFINITE-SET-008 Is the set of even natural numbers infinite?
- ZW-INFINITE-SET-009 Let f(n)=n+1 from ℕ to ℕ. Why does it prove that ℕ is infinite?