Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 3 - The Derivative - 3.4 Definition of the Derivative - 3.4 Exercises - Page 176: 29

Answer

$$ f(x)=e^{x} $$ Now use the rules for limits to get $$ \begin{split} f^{\prime}(x) &=\lim\limits_{h \to 0} \frac{f(x +h)- f(x)}{h}\\ &=\lim\limits_{h \to 0} \frac{e^{x+h}-e^{x} }{h}\\ &=\lim\limits_{h \to 0} \frac{e^{x}(e^{h}-1) }{h}\\ & \quad\quad\quad\quad[\text { by L'Hospital's Rule }] \\ &=e^{x} \end{split} $$ Use this result to find $$ f^{\prime}(2)=e^{2}=7.3891; $$ $$ f^{\prime}(16)=e^{16}= 8,886,111; $$ and $$ f^{\prime}(-3)=e^{-3}= 0.0498. $$

Work Step by Step

$$ f(x)=e^{x} $$ Go through the four steps to find $f^{\prime}(x)$ Step 1 Find $f(x+h)$ by replacing $x$ with $x +h$ $$ f(x +h)=e^{x+h} $$ Step 2 $$ f(x +h) -f(x)=e^{x+h}-e^{x} $$ Step 3 $$ \frac{f(x +h)- f(x)}{h}= \frac{e^{x+h}-e^{x} }{h} $$ Step 4 Now use the rules for limits to get $$ \begin{split} f^{\prime}(x) &=\lim\limits_{h \to 0} \frac{f(x +h)- f(x)}{h}\\ &=\lim\limits_{h \to 0} \frac{e^{x+h}-e^{x} }{h}\\ &=\lim\limits_{h \to 0} \frac{e^{x}(e^{h}-1) }{h}\\ & \quad\quad\quad\quad[\text { by L'Hospital's Rule }] \\ &=e^{x} \end{split} $$ Use this result to find $$ f^{\prime}(2)=e^{2}=7.3891, $$ $$ f^{\prime}(16)=e^{16}= 8,886,111 $$ and $$ f^{\prime}(-3)=e^{-3}= 0.0498 $$
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