Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 2 - Section 2.4 - The Precise Definition of a Limit - 2.4 Exercises - Page 114: 30

Answer

$\lim\limits_{x \to 2} (x^2+2x-7) = 1$

Work Step by Step

Let $\epsilon \gt 0$ be given. Let $\delta = min\{1, \frac{\epsilon}{7}\}$ Suppose that $\vert x-2 \vert \lt \delta$ Then: $\vert (x^2+2x-7) - 1\vert = \vert x^2+2x-8\vert = \vert (x+4)(x-2)\vert = \vert (x+4)\vert \cdot \vert(x-2)\vert \lt (7)(\delta) \leq (7)(\frac{\epsilon}{7}) = \epsilon$ Therefore, $\lim\limits_{x \to 2} (x^2+2x-7) = 1$
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