Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 13 - Vector Geometry - 13.5 Planes in 3-Space - Exercises - Page 685: 55



Work Step by Step

Since $ n_1=\langle 1,0,1\rangle $ and $ n_2=\langle -1,1,1\rangle $, we have \begin{align*} \cos \theta &=\frac{n_1 \cdot n_2}{\|n_1\|\|n_2\|}\\ &=\frac{-1+0+1}{\sqrt{1+0+1}\sqrt{1+1+1}}\\ &=\frac{0}{\sqrt{2}\sqrt{3}}\\ &=0. \end{align*} That is $$\theta=\frac{\pi}{2}.$$
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