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 - Preliminary Questions - Page 666: 2



Work Step by Step

The angle between two vectors $ u $ and $ v $ is given by $$\cos \theta=\frac{u \cdot v}{\|u\|\|u\|}$$ Now, if $ u \cdot v\lt0$, this means that $\cos \theta $ is negative, which means that the angle $\theta $ is in the second quadrant and therefore it is obtuse.
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