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: 19

Answer

\[\left\langle \pm \frac{3}{\sqrt{59}},\pm \frac{7}{\sqrt{59}},\pm \frac{1}{\sqrt{59}} \right\rangle \]

Work Step by Step

\[\begin{align} & \text{Let the vectors: }\mathbf{u}=-3\mathbf{i}+2\mathbf{j}-5\mathbf{k},\text{ }\mathbf{v}=\mathbf{i}-\mathbf{j}+4\mathbf{k} \\ & \\ & \text{Find }\mathbf{u}\times \mathbf{v} \\ & \mathbf{u}\times \mathbf{v}=\left| \begin{matrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ -3 & 2 & -5 \\ 1 & -1 & 4 \\ \end{matrix} \right| \\ & \mathbf{u}\times \mathbf{v}=\left| \begin{matrix} 2 & -5 \\ -1 & 4 \\ \end{matrix} \right|\mathbf{i}-\left| \begin{matrix} -3 & -5 \\ 1 & 4 \\ \end{matrix} \right|\mathbf{j}+\left| \begin{matrix} -3 & 2 \\ 1 & -1 \\ \end{matrix} \right|\mathbf{k} \\ & \mathbf{u}\times \mathbf{v}=3\mathbf{i}+7\mathbf{j}+\mathbf{k} \\ & \\ & \text{Finding a unit vector that is orthogonal to both }\mathbf{u}\text{ and }\mathbf{v} \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\pm \frac{3\mathbf{i}+7\mathbf{j}+\mathbf{k}}{\sqrt{{{\left( 3 \right)}^{2}}+{{\left( 7 \right)}^{2}}+{{\left( 1 \right)}^{2}}}} \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\pm \frac{1}{\sqrt{59}}\left( 3\mathbf{i}+7\mathbf{j}+\mathbf{k} \right) \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\pm \frac{3}{\sqrt{59}}\mathbf{i}+\frac{7}{\sqrt{59}}\mathbf{j}+\frac{1}{\sqrt{59}}\mathbf{k} \\ & or \\ & \frac{\mathbf{u}\times \mathbf{v}}{\left\| \mathbf{u}\times \mathbf{v} \right\|}=\left\langle \pm \frac{3}{\sqrt{59}},\pm \frac{7}{\sqrt{59}},\pm \frac{1}{\sqrt{59}} \right\rangle \\ \end{align}\]
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