Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 6 - Inverse Functions - 6.7 Hyperbolic Functions - 6.7 Exercises - Page 489: 13

Answer

\[\coth^2 x-1=\csc h^2x\]

Work Step by Step

To show that:-\[\coth^2 x-1=\csc h^2 x\] We know that \[\sinh x=\frac{e^x-e^{-x}}{2}\;\;\;...(1)\] and \[\cosh x=\frac{e^x+e^{-x}}{2}\;\;\;...(2)\] \[\csc h x=\frac{1}{\sinh x}\] Using (1) \[\Rightarrow \csc h x=\frac{2}{e^x-e^{-x}}\;\;\;...(3)\] \[\coth x=\frac{\cosh x}{\sinh x}\] Using (1) and (2) \[\coth x=\frac{e^{x}+e^{-x}}{e^{x}-e^{-x}}\] \[\Rightarrow \coth^2 x=\left(\frac{e^{x}+e^{-x}}{e^{x}-e^{-x}}\right)^2\] \[\Rightarrow \coth^2 x-1=\left(\frac{e^{x}+e^{-x}}{e^{x}-e^{-x}}\right)^2-1\] \[\Rightarrow \coth^2 x-1=\frac{(e^{x}+e^{-x})^2-(e^x-e^{-x})^2}{(e^{x}-e^{-x})^2}\] \[\Rightarrow \coth^2 x-1=\frac{2^2}{(e^{x}-e^{-x})^2}\] Using (3) \[\Rightarrow \coth^2 x-1=\csc h^2x\] Hence, \[\coth^2 x-1=\csc h^2x\]
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