Question 7 Let A be a subset of R'. Let A denote the intersection of all closed sets containing A. We call this the closure of A. (The book uses A-). (a) Prove that Ā = A iff A is closed. (b) Prove that ACĀ and A = A. (c) Prove AUB = AUB. %3D

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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#7 need a b and c
### Question 7

Let \( A \) be a subset of \( \mathbb{R}^p \). Let \( \overline{A} \) denote the intersection of all closed sets containing \( A \). We call this the **closure** of \( A \). (The book uses \( A^- \)).

#### (a) Prove that \( \overline{A} = A \) iff \( A \) is closed.

#### (b) Prove that \( A \subseteq \overline{A} \) and \( \overline{\overline{A}} = \overline{A} \).

#### (c) Prove \( A \cup B = \overline{A \cup B} \).
Transcribed Image Text:### Question 7 Let \( A \) be a subset of \( \mathbb{R}^p \). Let \( \overline{A} \) denote the intersection of all closed sets containing \( A \). We call this the **closure** of \( A \). (The book uses \( A^- \)). #### (a) Prove that \( \overline{A} = A \) iff \( A \) is closed. #### (b) Prove that \( A \subseteq \overline{A} \) and \( \overline{\overline{A}} = \overline{A} \). #### (c) Prove \( A \cup B = \overline{A \cup B} \).
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