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: 9



Work Step by Step

$$(i+j)\cdot (j+k)=i\cdot j+i\cdot k+j\cdot j+j\cdot k\\ =0+0+1+0=1.$$ Note that the product of $i\cdot j=i\cdot k=j\cdot k=0$, because they are perpendicular ($\theta=90^{\circ}$).
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