University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 2 - Section 2.3 - The Precise Definition of a Limit - Exercises - Page 75: 6

Answer

We take $\delta=0.2391$ here.

Work Step by Step

$$a=2.7591 \hspace{1cm} b=3.2391\hspace{1cm}c=3$$ Here we need to find $\delta\gt0$ such that for all $x$, $0\lt |x-3|\lt\delta$, then $2.7591\lt x\lt 3.2391$. The sketch is shown below. - From $3$ to $2.7591$: $3-2.7591=0.2409$ - From $3$ to $3.2391$: $3.2391-3=0.2391$ So the nearer endpoint of $(2.7591,3.2391)$ to $c=3$ is $3.2391$, and the distance is $0.2391$. So if we take $\delta=0.2391$ or any smaller positive value, then $0\lt |x-3|\lt0.2391$, and $x$ will only range in $(2.7609,3.2391)$, as shown by the red lines in the sketch, thereby $x$ is always placed between $2.7591$ and $3.2391$ as requested. In other words, $$0\lt |x-3|\lt0.2391\hspace{2cm}2.7591\lt x\lt 3.2391$$
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