Calculus, 10th Edition (Anton)

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

Chapter 0 - Before Calculus - 0.4 Inverse Functions - Exercises Set 0.4 - Page 45: 21

Answer

False

Work Step by Step

This statement is false. How do we know? Let $f$ be an invertible function such that $f(2) = 2$. Let's assume that $f^{-1}(2)=1/2$. The value of $f^{-1}(2)$ is the input to the function $f$ that produces an output of $2$. Since $f$ is invertible, we know that $f(f^{-1}(x)) = x$ for all $x$ in the domain of $f$. Therefore, $f(f^{-1}(2)) =2$, which means $f(1/2) = 2$. We got that to the value $y=2$ in the range of $f$ correspond two values of $x$ in the domain of $f$: $f(2)=f(1/2)=2$ This contradicts the fact that the function is one to one. So our assumption that $f^{-1}(2)=1/2$ is wrong. So, the correct statement is that $f^{-1}(2) = 2$, not $\frac{1}{2}$. Therefore, the statement "If $f$ is an invertible function such that $f(2) = 2$, then $f ^{−1}(2) = 1/2$" is false.
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