Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 7: Transcendental Functions - Section 7.1 - Inverse Functions and Their Derivatives - Exercises 7.1 - Page 373: 30

Answer

$$ f^{-1}(x) =\sqrt[3]{\frac{1}{x}} $$ Domain of $ f^{-1}$ is $(-\infty,0) \cup (0,\infty)$ Range of $ f^{-1}$ is $(-\infty,0) \cup (0,\infty)$

Work Step by Step

Given $$ f(x) =\frac{1}{x^{3}}$$ Find the inverse: $$y =\frac{1}{x^{3}} \\ x^{3} =\frac{1}{y} \\ x = \sqrt[3]{\frac{1}{y}} \\ \text {Switch } x \ and\ y, \text{}\\ y = \sqrt[3]{\frac{1}{x}} =f^{-1}(x)$$ We see that: Domain of $ f^{-1}$ is $(-\infty,0) \cup (0,\infty)$ and Range of $ f^{-1}$ is $(-\infty,0) \cup (0,\infty)$ Confirm the inverse: \begin{aligned} f\left(f^{-1}(x)\right) &=f\left(\frac{1}{\sqrt[3]{x}}\right) \\ &=\frac{1}{\left(\frac{1}{\sqrt[3]{x}}\right)^{3}} \\ &=\frac{1}{1/x} \\ &=x \\f^{-1}(f(x)) &=f^{-1}\left(\frac{1}{x^{3}}\right) \\ &=\frac{1}{\sqrt[3]{\frac{1}{x^{3}}}} \\ &=\frac{1}{\frac{1}{x}} \\ &=x \end{aligned}
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