Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 5 - Logarithmic, Exponential, and Other Transcendental Functions - 5.8 Exercises - Page 390: 16

Answer

$\displaystyle \sinh x=\frac{\sqrt{3}}{3}$ $\mathrm{c}\mathrm{s}\mathrm{c}\mathrm{h} x=\sqrt{3}$ $\displaystyle \cosh x=\frac{2\sqrt{3}}{3}$ $\displaystyle \mathrm{s}\mathrm{e}\mathrm{c}\mathrm{h}x=\frac{\sqrt{3}}{2}$ $\coth x=2$

Work Step by Step

$\begin{align*} \tanh^{2}x+{\rm sech}^{2}x&=1\\ {\rm sech}^{2}x&=1-\tanh^{2}x \\ {\rm sech}^{2}x&=1-\displaystyle \frac{1}{4} \\\\ {\rm sech} x&=\sqrt{3/4} \\\\ & =\displaystyle \frac{\sqrt{3}}{2} \end{align*}$ $\displaystyle \mathrm{s}\mathrm{e}\mathrm{c}\mathrm{h}x=\frac{\sqrt{3}}{2}$ $\displaystyle \cosh x=\frac{1}{{\rm sech} x}=\frac{2}{\sqrt{3}}\cdot\frac{\sqrt{3}}{\sqrt{3}}=\frac{2\sqrt{3}}{3}$ $\displaystyle \coth x=\frac{1}{\tanh x}=\frac{1}{1/2}=2$ $\displaystyle \sinh x=\tanh x\cosh x=\frac{1}{2}\cdot\frac{2\sqrt{3}}{3}=\frac{\sqrt{3}}{3}$ $\mathrm{c}\mathrm{s}\mathrm{c}\mathrm{h} x=\displaystyle \frac{1}{\sqrt{3}/3}=\sqrt{3}$
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