Exercise · ZW-HEINE-BOREL-THEOREM-008 · ★★☆ Intermediate
Let \(A=[0,1]\), \(B=(0,1)\), \(C=\mathbb{Z}\), \(D=\{0\}\cup\{1/n:n\ge1\}\) in \(\mathbb{R}\). How many are compact?
Choose one option.
Show answer
- C. \(2\)
Explanation
\(A\) and \(D\) are closed and bounded. \(B\) is not closed and \(C\) is not bounded.
Review the concept: Heine-Borel theorem
A subset \(K\) of \(\mathbb{R}^n\) with the usual metric is compact if and only if it is closed and bounded.
\[K\subseteq\mathbb{R}^n\ \text{compact}\iff K\ \text{closed and bounded}\]
More practice problems: heine-borel theorem
- ZW-HEINE-BOREL-THEOREM-001 Identify the compact subset of ℝ:
- ZW-HEINE-BOREL-THEOREM-002 Which of these subsets of ℝ^2 is compact?
- ZW-HEINE-BOREL-THEOREM-003 Why is [0,∞) not compact in ℝ?
- ZW-HEINE-BOREL-THEOREM-004 Why is (0,1] not compact in ℝ?
- ZW-HEINE-BOREL-THEOREM-005 Among these plane figures, which one is compact?
- ZW-HEINE-BOREL-THEOREM-006 Which of these subsets of ℝ is compact?
- ZW-HEINE-BOREL-THEOREM-007 Which of these subsets of ℝ^3 is compact?
- ZW-HEINE-BOREL-THEOREM-009 The metric space X=(0,1) with the usual distance is closed (in itself) and bounded. Is it compact?