Prove that essays (a) If A is open and B is closed, then A - B is open; (b) If A is closed and B is open, then A - B is closed.
Prove that essays (a) If A is open and B is closed, then A - B is open; (b) If A is closed and B is open, then A - B is closed.
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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![### Problem Statement:
**Prove that:**
(a) If \( A \) is open and \( B \) is closed, then \( A - B \) is open;
(b) If \( A \) is closed and \( B \) is open, then \( A - B \) is closed.
### Explanation:
This problem involves concepts from topology, specifically dealing with the sets and their properties in terms of openness and closedness. In this context, the subtraction \( A - B \) refers to the set difference, which is the set of elements in \( A \) that are not in \( B \).
### Detailed Explanation:
- **Open Set**: A set is open if, roughly speaking, for every point within the set, there is a surrounding "neighborhood" that is entirely contained within the set.
- **Closed Set**: A set is closed if it contains all its limit points, or equivalently, its complement within a given space is open.
### To Prove:
1. **(a) \( A - B \) is Open**:
- Given: \( A \) is open, \( B \) is closed.
- Objective: Show that the difference \( A - B \) is open.
- Strategy: Use properties of open and closed sets in a given topological space to demonstrate that removing a closed set from an open set results in an open set.
2. **(b) \( A - B \) is Closed**:
- Given: \( A \) is closed, \( B \) is open.
- Objective: Show that the difference \( A - B \) is closed.
- Strategy: Use the concept of complements and properties of closed sets to show that the removal of an open set from a closed set results in a closed set.
This theoretical approach is fundamental in various branches of mathematics, including analysis and topology, and has applications in fields like functional analysis and metric space theory.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fca338f80-b963-4565-b3ff-b52dc3ed88af%2F8fe48723-933d-48b8-a161-7d0b3ce9aff6%2Fn2258n_processed.jpeg&w=3840&q=75)
Transcribed Image Text:### Problem Statement:
**Prove that:**
(a) If \( A \) is open and \( B \) is closed, then \( A - B \) is open;
(b) If \( A \) is closed and \( B \) is open, then \( A - B \) is closed.
### Explanation:
This problem involves concepts from topology, specifically dealing with the sets and their properties in terms of openness and closedness. In this context, the subtraction \( A - B \) refers to the set difference, which is the set of elements in \( A \) that are not in \( B \).
### Detailed Explanation:
- **Open Set**: A set is open if, roughly speaking, for every point within the set, there is a surrounding "neighborhood" that is entirely contained within the set.
- **Closed Set**: A set is closed if it contains all its limit points, or equivalently, its complement within a given space is open.
### To Prove:
1. **(a) \( A - B \) is Open**:
- Given: \( A \) is open, \( B \) is closed.
- Objective: Show that the difference \( A - B \) is open.
- Strategy: Use properties of open and closed sets in a given topological space to demonstrate that removing a closed set from an open set results in an open set.
2. **(b) \( A - B \) is Closed**:
- Given: \( A \) is closed, \( B \) is open.
- Objective: Show that the difference \( A - B \) is closed.
- Strategy: Use the concept of complements and properties of closed sets to show that the removal of an open set from a closed set results in a closed set.
This theoretical approach is fundamental in various branches of mathematics, including analysis and topology, and has applications in fields like functional analysis and metric space theory.
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