Let (xn) be a bounded sequence and let s = sup{xn : n e N}. Show that if s ¢ {xn : n E N}, then there is a subsequence of (xn) that converges to s. (Hint: Use Lemma 1.5.1 and use s - 1< s, s- 1/2 < s, s – 1/3 < s, ...)

Advanced Engineering Mathematics
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Chapter2: Second-order Linear Odes
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**Lemma 1.5.1**

An upper bound \( u \) is the supremum of \( S \) in \( \mathbb{R} \) if and only if \( \forall \, \varepsilon > 0, \exists \, a \in S \) such that \( u - \varepsilon < a \).

**Diagram Explanation:**

The diagram is a number line representing the concept of the supremum \( u \) of a set \( S \) within the real numbers \( \mathbb{R} \). 

- The area marked \( S \) indicates elements within the set.
- The number 0 is labeled for reference on the line.
- The point \( u - \varepsilon \) is depicted as a mark on the number line left of \( a \).
- The element \( a \) from the set \( S \) is shown as being greater than \( u - \varepsilon \).
- The supremum \( u = \sup S \) indicates the least upper bound, positioned to show its relation to the set \( S \).

This visualization emphasizes that for every positive \( \varepsilon \), you can find an element \( a \) in \( S \) that is greater than \( u - \varepsilon \), affirming \( u \) as the supremum of \( S \).
Transcribed Image Text:**Lemma 1.5.1** An upper bound \( u \) is the supremum of \( S \) in \( \mathbb{R} \) if and only if \( \forall \, \varepsilon > 0, \exists \, a \in S \) such that \( u - \varepsilon < a \). **Diagram Explanation:** The diagram is a number line representing the concept of the supremum \( u \) of a set \( S \) within the real numbers \( \mathbb{R} \). - The area marked \( S \) indicates elements within the set. - The number 0 is labeled for reference on the line. - The point \( u - \varepsilon \) is depicted as a mark on the number line left of \( a \). - The element \( a \) from the set \( S \) is shown as being greater than \( u - \varepsilon \). - The supremum \( u = \sup S \) indicates the least upper bound, positioned to show its relation to the set \( S \). This visualization emphasizes that for every positive \( \varepsilon \), you can find an element \( a \) in \( S \) that is greater than \( u - \varepsilon \), affirming \( u \) as the supremum of \( S \).
Let \((x_n)\) be a bounded sequence and let \(s = \sup\{x_n: n \in \mathbb{N}\}\). Show that if \(s \not\in \{x_n: n \in \mathbb{N}\}\), then there is a subsequence of \((x_n)\) that converges to \(s\). (Hint: Use Lemma 1.5.1 and use \(s - 1 < s, \, s - 1/2 < s, \, s - 1/3 < s, \ldots\))
Transcribed Image Text:Let \((x_n)\) be a bounded sequence and let \(s = \sup\{x_n: n \in \mathbb{N}\}\). Show that if \(s \not\in \{x_n: n \in \mathbb{N}\}\), then there is a subsequence of \((x_n)\) that converges to \(s\). (Hint: Use Lemma 1.5.1 and use \(s - 1 < s, \, s - 1/2 < s, \, s - 1/3 < s, \ldots\))
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