
Advanced Engineering Mathematics
10th Edition
ISBN: 9780470458365
Author: Erwin Kreyszig
Publisher: Wiley, John & Sons, Incorporated
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Transcribed Image Text:**Title: Proving the Openness of the Interval \(E = (a, +\infty)\) in \(\mathbb{R}\)**
**Objective:**
To prove that the interval \(E = (a, +\infty)\) is an open set in the real number system \(\mathbb{R}\). We will show all the details of the proof.
**Introduction to Open Sets:**
In the context of real numbers, a set \(S\) is open if, for every point \(x \in S\), there exists an \(\epsilon > 0\) such that the interval \((x - \epsilon, x + \epsilon) \subseteq S\).
**Proof:**
We need to show that for any \(x \in (a, +\infty)\), there exists an \(\epsilon > 0\) for which \((x - \epsilon, x + \epsilon) \subseteq (a, +\infty)\).
1. **Choose any \(x \in (a, +\infty)\).**
- By definition, \(x > a\).
2. **Define \(\epsilon = \frac{x - a}{2}\).**
- Since \(x > a\), \(\epsilon\) is positive.
3. **Consider the interval \((x - \epsilon, x + \epsilon)\).**
- Calculate \(x - \epsilon = x - \frac{x - a}{2} = \frac{2x - x + a}{2} = \frac{x + a}{2}\).
- Note that \(\frac{x + a}{2} > a\) because \(x > a\).
4. **Verify that \((x - \epsilon, x + \epsilon) \subseteq (a, +\infty)\):**
- From above, \(x - \epsilon = \frac{x + a}{2} > a\), ensuring \(x - \epsilon > a\).
- Therefore, the entire interval \((x - \epsilon, x + \epsilon)\) is contained within \((a, +\infty)\).
**Conclusion:**
Since for every \(x \in (a, +\infty)\), there exists an \(\epsilon > 0\) such that \((x - \epsilon, x + \epsilon
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