Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 17 - Line and Surface Integrals - Chapter Review Exercises - Page 971: 39

Answer

$\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = 4\ln \left( {1 + {{\left( {\ln 2} \right)}^4} + {{\rm{e}}^2}} \right)$

Work Step by Step

We have $f\left( {x,y,z} \right) = 4{x^2}\ln \left( {1 + {y^4} + {z^2}} \right)$ and the path: ${\bf{r}}\left( t \right) = \left( {{t^3},\ln \left( {1 + {t^2}} \right),{{\rm{e}}^t}} \right)$ for $0 \le t \le 1$ Evaluate: $f\left( {{\bf{r}}\left( t \right)} \right) = 4{t^6}\ln \left( {1 + {{\left[ {\ln \left( {1 + {t^2}} \right)} \right]}^4} + {{\rm{e}}^{2t}}} \right)$ Since there is a potential function $f$ such that ${\bf{F}} = \nabla f$, we call ${\bf{F}}$ conservative. Thus, the line integral of ${\bf{F}}$ along the path ${\bf{r}}\left( t \right) = \left( {{t^3},\ln \left( {1 + {t^2}} \right),{{\rm{e}}^t}} \right)$ for $0 \le t \le 1$, depends only on the endpoints, that is $\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = f\left( {{\bf{r}}\left( 1 \right)} \right) - f\left( {{\bf{r}}\left( 0 \right)} \right)$ $\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = 4\ln \left( {1 + {{\left( {\ln 2} \right)}^4} + {{\rm{e}}^2}} \right) - 0$ So, $\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = 4\ln \left( {1 + {{\left( {\ln 2} \right)}^4} + {{\rm{e}}^2}} \right)$.
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