Linear Algebra: A Modern Introduction

Published by Cengage Learning
ISBN 10: 1285463242
ISBN 13: 978-1-28546-324-7

Chapter 1 - Vectors - 1.2 Length and Angle: The Dot Product - Exercises 1.2 - Page 290: 28

Answer

$\Theta \;=\;97^\circ 25^{'}$

Work Step by Step

$u=[1\;,2\;,3\;,4]\;\;\;\;\;\;\;\;\;v=\;[-3\;,1\;,2\;,-2]\\\\$ $cos \;\Theta\;=\frac{u\;.\;v}{\left \| u \right \|\;.\;\left \| v \right \|} \\\\$ $u\;.v\;=\;(1)(-3)\;+\;(2)(1)\;+\;(3)(2)\;+\;(4)(-2)\;=\;-3\\\\$ $\left \| u \right \|\;=\;\sqrt{(1)^2\;+(2)^2\;+(3)^2\;+(4)^2}\;=\;\sqrt{30}\\\\$ $\left \| v \right \|\;=\;\sqrt{(-3)^2\;+(1)^2\;+(2)^2\;+(-2)^2}\;=\;3\sqrt{2}\\\\$ $cos \;\Theta\;=\frac{u\;.\;v}{\left \| u \right \|\;.\;\left \| v \right \|}\;=\;\frac{-3}{(\sqrt{30})(3\sqrt{2})}\\\\$ $cos \;\Theta\;=\frac{-\sqrt{60}}{60}\\\\$ $\Theta \;=\;cos^{-1}(\frac{-\sqrt{60}}{60})\;=\;97^\circ 25^{'}$
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