Calculus (3rd Edition)

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

Chapter 13 - Vector Geometry - 13.3 Dot Product and the Angle Between Two Vectors - Exercises - Page 666: 13


The angle between the vectors is obtuse.

Work Step by Step

Since $$\langle 1,1,1\rangle \cdot \langle 1,-2,-2\rangle =1-2-2=-3\neq 0$$ then the vectors are not orthogonal. The angle between the vectors is obtuse since their dot product is negative (negative cosine of the dot product indicates that we are in the 2nd quadrant).
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