University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 4 - Section 4.2 - The Mean Value Theorem - Exercises - Page 223: 13

Answer

$f(x)$ does not satisfy the hypotheses because $f'(x)$ is not defined on the whole interval $(-2,0)$ (f is not differentiable at $x=-1$).

Work Step by Step

The Mean Value Theorem requires - that $f(x)$ is continuous on $[a,b]$ - that $f'(x)$ is defined on $(a,b)$ Here, $[a,b]=[-2,0]$ Polynomials are continuous functions. The only problem might arise at $x=-1.$ $\displaystyle \lim_{x\rightarrow 0^{-}}f(x)=(-1)^{2}-(-1)=2$ $\displaystyle \lim_{x\rightarrow 0^{+}}f(x)=2(-1)^{2}-3(-1)-3=2$ and, $f(-1)=2$, so f is continuous on $[-2,0]$. $f'(x)=\left\{\begin{array}{ll} 2x-1, & -2\leq x\leq-1\\ 4x-3 & -1\lt x\leq 0 \end{array}\right.$ $\displaystyle \lim_{x\rightarrow 0^{-}}f'(x)=2(-1)-1=-3$ $\displaystyle \lim_{x\rightarrow 0^{+}}f'(x)=4(-1)-3=-7$ So, the derivative is not defined at $x=-1$.
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