Calculus: Early Transcendentals 8th Edition

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

Chapter 5 - Review - Exercises - Page 423: 49

Answer

$$ y=\int_{\sqrt{x}}^{x} \frac{e^{t}}{t} d t $$ The derivative of the given function is $$ \frac{d y}{d x}=-\frac{e^{\sqrt{x}}}{2 x} +\frac{e^{x}}{x}=\frac{2e^{x}-e^{\sqrt{x}}}{2x} $$

Work Step by Step

$$ y=\int_{\sqrt{x}}^{x} \frac{e^{t}}{t} d t $$ $$ \begin{split} y &=\int_{\sqrt{x}}^{x} \frac{e^{t}}{t} d t \\ & =\int_{\sqrt{x}}^{1} \frac{e^{t}}{t} d t+\int_{1}^{x} \frac{e^{t}}{t} d t \\ & =-\int_{1}^{\sqrt{x}} \frac{e^{t}}{t} d t+\int_{1}^{x} \frac{e^{t}}{t} d t \end{split} $$ $ \Rightarrow $ $$ \frac{d y}{d x}=-\frac{d}{d x}\left(\int_{1}^{\sqrt{x}} \frac{e^{t}}{t} d t\right)+\frac{d}{d x}\left(\int_{1}^{x} \frac{e^{t}}{t} d t\right) $$ Let $ u = \sqrt {x}$ . Then $$ \begin{split} \frac{d}{d x} \int_{1}^{\sqrt{x}} \frac{e^{t}}{t} d t&=\frac{d}{d x} \int_{1}^{u} \frac{e^{t}}{t} d t \\ &=\frac{d}{d u}\left(\int_{1}^{u} \frac{e^{t}}{t} d t\right) \frac{d u}{d x} \\ &=\frac{e^{u}}{u} \cdot \frac{1}{2 \sqrt{x}} \\ &=\frac{e^{\sqrt{x}}}{\sqrt{x}} \cdot \frac{1}{2 \sqrt{x}} \\ &=\frac{e^{\sqrt{x}}}{2 x} \end{split} $$ so, the derivative of the given function is $$ \frac{d y}{d x}=-\frac{e^{\sqrt{x}}}{2 x} +\frac{e^{x}}{x}=\frac{2e^{x}-e^{\sqrt{x}}}{2x} $$
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