Let an be a bounded sequence of real numbers. Let s = sup{an: n ≥ 1} {ann € N}. Show that there is a subsequence of an that and s increases to s.

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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Let an be a bounded sequence of real numbers. Let s = sup {an : n ≥ 1} and s ∈/ {an : n ∈ N}. Show that there is a subsequence of an that increases to s.
**Problem Statement**

Let \( a_n \) be a bounded sequence of real numbers. Let \( s = \sup \{ a_n : n \geq 1 \} \) and \( s \notin \{ a_n : n \in \mathbb{N} \} \). Show that there is a subsequence of \( a_n \) that increases to \( s \).

**Explanation**

- **\( a_n \):** A sequence of real numbers that is bounded.
- **\( s = \sup \{ a_n : n \geq 1 \} \):** The supremum (least upper bound) of the sequence.
- **\( s \notin \{ a_n : n \in \mathbb{N} \} \):** The value \( s \) is not an element of the sequence. 

**Objective**

Demonstrate that there exists a subsequence of \( a_n \) which converges to \( s \).

This type of problem often arises in the context of real analysis, focusing on properties of sequences and their limits. The goal is to use the definition of supremum and subsequences to highlight the existence of such a convergent subsequence.
Transcribed Image Text:**Problem Statement** Let \( a_n \) be a bounded sequence of real numbers. Let \( s = \sup \{ a_n : n \geq 1 \} \) and \( s \notin \{ a_n : n \in \mathbb{N} \} \). Show that there is a subsequence of \( a_n \) that increases to \( s \). **Explanation** - **\( a_n \):** A sequence of real numbers that is bounded. - **\( s = \sup \{ a_n : n \geq 1 \} \):** The supremum (least upper bound) of the sequence. - **\( s \notin \{ a_n : n \in \mathbb{N} \} \):** The value \( s \) is not an element of the sequence. **Objective** Demonstrate that there exists a subsequence of \( a_n \) which converges to \( s \). This type of problem often arises in the context of real analysis, focusing on properties of sequences and their limits. The goal is to use the definition of supremum and subsequences to highlight the existence of such a convergent subsequence.
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