Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 6 - Section 6.7 - The Dot Product - Exercise Set - Page 792: 5

Answer

$\mathbf{v}\cdot \mathbf{w}=100$ and $\mathbf{v}\cdot \mathbf{v}=61$

Work Step by Step

The dot product, $\mathbf{v}\cdot \mathbf{w}$ as, $\begin{align} & \mathbf{v}\cdot \mathbf{w=}\left( -6\mathbf{i}-5\mathbf{j} \right)\cdot \left( -10\mathbf{i}-8\mathbf{j} \right) \\ & =\left( -6 \right)\mathbf{i}\cdot \left( -10 \right)\mathbf{i+}\left( -6 \right)\mathbf{i}\cdot \left( -8 \right)\mathbf{j+}\left( -5 \right)\mathbf{j}\cdot \left( -10 \right)\mathbf{i+}\left( -5 \right)\mathbf{j}\cdot \left( -8 \right)\mathbf{j} \\ & =60\left( \mathbf{i}\cdot \mathbf{i} \right)+48\left( \mathbf{i}\cdot \mathbf{j} \right)+50\left( \mathbf{j}\cdot \mathbf{i} \right)+40\left( \mathbf{j}\cdot \mathbf{j} \right) \\ & =60\left( 1 \right)+48\left( 0 \right)+50\left( 0 \right)+40\left( 1 \right) \end{align}$ Solve ahead to get the result as, $\begin{align} & \mathbf{v}\cdot \mathbf{w}=60\left( 1 \right)+48\left( 0 \right)+50\left( 0 \right)+40\left( 1 \right) \\ & =60+0+0+40 \\ & =100 \end{align}$ The dot product, $\mathbf{v}\cdot \mathbf{v}$ as, $\begin{align} & \mathbf{v}\cdot \mathbf{v=}\left( -6\mathbf{i}-5\mathbf{j} \right)\cdot \left( -6\mathbf{i}-5\mathbf{j} \right) \\ & =\left( -6 \right)\mathbf{i}\cdot \left( -6 \right)\mathbf{i+}\left( -6 \right)\mathbf{i}\cdot \left( -5 \right)\mathbf{j+}\left( -5 \right)\mathbf{j}\cdot \left( -6 \right)\mathbf{i+}\left( -5 \right)\mathbf{j}\cdot \left( -5 \right)\mathbf{j} \\ & =36\left( \mathbf{i}\cdot \mathbf{i} \right)+30\left( \mathbf{i}\cdot \mathbf{j} \right)+30\left( \mathbf{j}\cdot \mathbf{i} \right)+25\left( \mathbf{j}\cdot \mathbf{j} \right) \\ & =36\left( 1 \right)+30\left( 0 \right)+30\left( 0 \right)+25\left( 1 \right) \end{align}$ Solve ahead to get the result as, $\begin{align} & \mathbf{v}\cdot \mathbf{v}=36\left( 1 \right)+30\left( 0 \right)+30\left( 0 \right)+25\left( 1 \right) \\ & =36+0+0+25 \\ & =61 \end{align}$
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