Answer
$$1$$
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 ($\theta=90^{\circ}$).
Calculus (3rd Edition)
by Rogawski, Jon; Adams, Colin
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
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