Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 1 - Limits and Continuity - 1.3 Limits At Infinity; End Behavior Of A Function - Exercises Set 1.3 - Page 79: 35

Answer

Answer: 1

Work Step by Step

$\lim\limits_{x \to \infty} \frac{e^x + e^{-x}}{e^x- e^{-x}}$ First, we simply this limit. $\frac{e^x + e^{-x}}{e^x- e^{-x}} = \frac{e^x + \frac{1}{e^{x}}}{e^x - \frac{1}{e^{x}}}$ (Because $e^{-x} = \frac{1}{e^x}$) Thus, we have: $\frac{\frac{e^{2x} + 1}{e^x}}{\frac{e^{2x} - 1}{e^x}} = \frac{e^{2x} + 1}{e^{2x} - 1}$. Dividing both numerator and denominator by $e^{2x}$, we have: $\frac{1 +\frac{1}{e^{2x}}}{1 -\frac{1}{e^{2x}}}$. We know that $\lim\limits_{x \to \infty} e^{x} = \infty$ Hence, $\lim\limits_{x \to \infty} e^{2x} = \infty$ Hence, Hence, $\lim\limits_{x \to \infty} \frac{1}{e^{2x}} = 0$. Thus, $\lim\limits_{x \to \infty} \frac{1 +\frac{1}{e^{2x}}}{1 -\frac{1}{e^{2x}}} = \frac{1 + 0}{1 - 0} = 1$
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