Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 11 - Vectors and the Geometry of Space - 11.4 Exercises - Page 781: 18

Answer

\[\frac{5}{3\sqrt{22}}\mathbf{i}+\frac{2}{3\sqrt{22}}\mathbf{j}+\frac{13}{3\sqrt{22}}\mathbf{k}\]

Work Step by Step

\[\begin{align} & \text{Let the vectors be: }\mathbf{u}=\left\langle -8,-6,4 \right\rangle ,\text{ }\mathbf{v}=\left\langle 10,-12,-2 \right\rangle \\ & \\ & \text{Find }\mathbf{u}\times \mathbf{v} \\ & \mathbf{u}\times \mathbf{v}=\left| \begin{matrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ -8 & -6 & 4 \\ 10 & -12 & -2 \\ \end{matrix} \right| \\ & \mathbf{u}\times \mathbf{v}=\left| \begin{matrix} -6 & 4 \\ -12 & -2 \\ \end{matrix} \right|\mathbf{i}-\left| \begin{matrix} -8 & 4 \\ 10 & -2 \\ \end{matrix} \right|\mathbf{j}+\left| \begin{matrix} -8 & -6 \\ 10 & -12 \\ \end{matrix} \right|\mathbf{k} \\ & \mathbf{u}\times \mathbf{v}=60\mathbf{i}+24\mathbf{j}+156\mathbf{k} \\ & \\ & \text{Finding a unit vector that is orthogonal to both }\mathbf{u}\text{ and }\mathbf{v} \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\frac{60\mathbf{i}+24\mathbf{j}+156\mathbf{k}}{\sqrt{{{\left( 60 \right)}^{2}}+{{\left( 24 \right)}^{2}}+{{\left( 156 \right)}^{2}}}} \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\frac{1}{\sqrt{28512}}\left( 60\mathbf{i}+24\mathbf{j}+156\mathbf{k} \right) \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\frac{1}{36\sqrt{22}}\left( 60\mathbf{i}+24\mathbf{j}+156\mathbf{k} \right) \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\frac{5}{3\sqrt{22}}\mathbf{i}+\frac{2}{3\sqrt{22}}\mathbf{j}+\frac{13}{3\sqrt{22}}\mathbf{k} \\ \end{align}\]
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