Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 4 - Section 4.2 - The Mean Value Theorem - 4.2 Exercises - Page 292: 27

Answer

No function $f$ exists such that $f(0) = -1$, $f(2) = 4$, and $f'(x) \leq 2$ for all $x$.

Work Step by Step

Let's assume that $f'(x) \leq 2$ for all $x$ Since $f$ is differentiable for all $x$ then $f$ is continuous for all $x$. Then $f$ is continuous and differentiable on the interval $[0,2]$ According to the Mean Value Theorem, there is a number $c$ in the interval $(0,2)$ such that $f'(c) = \frac{f(2)-f(0)}{2-0} = \frac{4-(-1)}{2} = \frac{5}{2}$ However, this contradicts our assumption that $f'(x) \leq 2$ for all $x$. Therefore, no function $f$ exists such that $f(0) = -1$, $f(2) = 4$, and $f'(x) \leq 2$ for all $x$.
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