Calculus (3rd Edition)

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

Chapter 14 - Calculus of Vector-Valued Functions - 14.2 Calculus of Vector-Valued Functions - Exercises - Page 720: 28

Answer

$\frac{d}{{ds}}{\bf{v}}\left( {g\left( s \right)} \right){|_{s = 4}} = - 54{\bf{i}} - 18{\bf{j}} + 6{\bf{k}}$

Work Step by Step

We have ${\bf{v}}\left( s \right) = {s^2}{\bf{i}} + 2s{\bf{j}} + 9{s^{ - 2}}{\bf{k}}$. So, ${\bf{v}}'\left( s \right) = 2s{\bf{i}} + 2{\bf{j}} - 18{s^{ - 3}}{\bf{k}}$ Using the Chain Rule on $\frac{d}{{ds}}{\bf{v}}\left( {g\left( s \right)} \right)$ gives $\frac{d}{{ds}}{\bf{v}}\left( {g\left( s \right)} \right) = {\bf{v}}'\left( {g\left( s \right)} \right)g'\left( s \right)$ Evaluate $\frac{d}{{ds}}{\bf{v}}\left( {g\left( s \right)} \right)$ at $s=4$. $\frac{d}{{ds}}{\bf{v}}\left( {g\left( s \right)} \right){|_{s = 4}} = {\bf{v}}'\left( {g\left( 4 \right)} \right)g'\left( 4 \right)$ Since $g\left( 4 \right) = 3$ and $g'\left( 4 \right) = - 9$, so $\frac{d}{{ds}}{\bf{v}}\left( {g\left( s \right)} \right){|_{s = 4}} = - 9{\bf{v}}'\left( 3 \right) = - 9\left( {6{\bf{i}} + 2{\bf{j}} - \frac{{18}}{{27}}{\bf{k}}} \right)$ $\frac{d}{{ds}}{\bf{v}}\left( {g\left( s \right)} \right){|_{s = 4}} = - 54{\bf{i}} - 18{\bf{j}} + 6{\bf{k}}$
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