Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 11 - Three-Dimensional Space; Vectors - 11.4 Cross Product - Exercises Set 11.4 - Page 804: 22

Answer

\[ 29=(\vec{w} \times \vec{v})\cdot\vec{u} \]

Work Step by Step

To evaluate $ (\vec{w} \times \vec{v})\cdot \vec{u}$, we can use the following formula. \[ (\vec{w} \times \vec{v})\cdot\vec{u}=\left|\begin{array}{lll} u_{1} & u_{2} & u_{3} \\ v_{1} & v_{2} & v_{3} \\ w_{1} & w_{2} & w_{3} \end{array}\right| \] It's given that \[ \vec{w}=(-4,1,-3) , \vec{v}=\langle 0,3,2\rangle \text { and } \vec{u}=(1,-2,2) \] And then, \[ \begin{aligned} (\vec{w} \times \vec{v}) \cdot \vec{u}&=\left|\begin{array}{ccc} 1 & -2 & 2 \\ 0 & 3 & 2 \\ -4 & 1 & -3 \end{array}\right| \\ &=0\left|\begin{array}{cc} -2 & 2 \\ 1 & -3 \end{array}\right|+3\left|\begin{array}{cc} 1 & 2 \\ -4 & -3 \end{array}\right|-2\left|\begin{array}{cc} 1 & -2 \\ -4 & 1 \end{array}\right| \\ &=-2(1-8)+3(8-3) \\ &=14+15=29 \end{aligned} \] We have found that: \[ 29= (\vec{w} \times \vec{v})\cdot\vec{u} \]
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