Show that lim supa is the largest subsequence limit of {a} by showing that (1) there is some subsequence of {a} which converges to lim supa, but (2) if a > lim sup there is no subsequence of {a} which converges to α. Assume lim sup ± 00 12-00 n 11-0011 a then

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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**Transcribed Text:**

Show that \( \limsup_{n \to \infty} a_n \) is the largest subsequence limit of \( \{a_n\} \) by showing that (1) there is some subsequence of \( \{a_n\} \) which converges to \( \limsup_{n \to \infty} a_n \), but (2) if \( \alpha > \limsup_{n \to \infty} a_n \) then there is no subsequence of \( \{a_n\} \) which converges to \( \alpha \). Assume \( \limsup_{n \to \infty} a_n \neq \pm \infty \).

**Explanation:**

This problem involves the concept of the limit superior (\( \limsup \)) of a sequence \( \{a_n\} \), which is a key concept in real analysis. The task is to demonstrate two key properties:

1. There exists a subsequence of the sequence \( \{a_n\} \) that converges precisely to \( \limsup_{n \to \infty} a_n \).

2. If any number \( \alpha \) is greater than \( \limsup_{n \to \infty} a_n \), then no subsequence of \( \{a_n\} \) converges to \( \alpha \).

The assumption \( \limsup_{n \to \infty} a_n \neq \pm \infty \) ensures that the limit superior is finite, making the problem tractable.

This exercise is a common question in advanced calculus or real analysis courses, as it explores the limiting behavior of sequences and subsequences.
Transcribed Image Text:**Transcribed Text:** Show that \( \limsup_{n \to \infty} a_n \) is the largest subsequence limit of \( \{a_n\} \) by showing that (1) there is some subsequence of \( \{a_n\} \) which converges to \( \limsup_{n \to \infty} a_n \), but (2) if \( \alpha > \limsup_{n \to \infty} a_n \) then there is no subsequence of \( \{a_n\} \) which converges to \( \alpha \). Assume \( \limsup_{n \to \infty} a_n \neq \pm \infty \). **Explanation:** This problem involves the concept of the limit superior (\( \limsup \)) of a sequence \( \{a_n\} \), which is a key concept in real analysis. The task is to demonstrate two key properties: 1. There exists a subsequence of the sequence \( \{a_n\} \) that converges precisely to \( \limsup_{n \to \infty} a_n \). 2. If any number \( \alpha \) is greater than \( \limsup_{n \to \infty} a_n \), then no subsequence of \( \{a_n\} \) converges to \( \alpha \). The assumption \( \limsup_{n \to \infty} a_n \neq \pm \infty \) ensures that the limit superior is finite, making the problem tractable. This exercise is a common question in advanced calculus or real analysis courses, as it explores the limiting behavior of sequences and subsequences.
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