University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 9 - Section 9.1 - Sequences - Exercises - Page 489: 119

Answer

$\{a_{n}\}$ diverges.

Work Step by Step

For odd n, $a_{n}=0$ For even n, $a_{n}=2\displaystyle \cdot\frac{n+1}{n}=2(1+\frac{1}{n})$ Let $\epsilon=1/2\gt 0.$ The sequence of even-indexed terms converges to $2$, and the sequence of odd-indexed terms converges to $0$. If there were a limit L, then there would exist an index N, after which $|L-a_{n}|\lt 1/2$ Every other (odd-indexed) term of the sequence is zero, so it follows that $|L-0|\lt 1/2$ $L=(-\displaystyle \frac{1}{2},\frac{1}{2})$ But, since every other (even-indexed) term approaches 2, it would have to be that $L\in(1.5,2.5)$ to satisfy the condition $|L-a_{n}|\lt\epsilon$. L can't be in both these intervals, so it does not exist. $\{a_{n}\}$ does not have a limit$\Rightarrow$it diverges.
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