Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 12 - Vectors and the Geometry of Space - Review - Exercises - Page 882: 9


$cos^{-1}\dfrac{1}{3}\approx 70.53 ^\circ$

Work Step by Step

$a_1=\lt 1,1,1 \gt$ and $a_2= \lt 1,-1,1 \gt$ $|a_1|=|a_2|=\sqrt {1+1+1}= \sqrt3$ $a_1a_2=|a_1||a_2| cos \theta$ $ cos \theta=\frac{\lt 1,1,1 \gt \cdot \lt 1,-1,1 \gt }{\sqrt3}$ $ cos \theta=\dfrac{1}{3}$ $\theta = cos^{-1}\dfrac{1}{3}\approx 70.53 ^\circ$
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