Answer
$1.$
Work Step by Step
$$
\left|\begin{array}{rrr}{\cos \theta} & {\sin \theta} \\ {-\sin \theta} & {\cos \theta}\end{array}\right|=\cos^2 \theta+\sin^2 \theta=1.
$$
Elementary Linear Algebra 7th Edition
by Larson, Ron
Published by
Cengage Learning
ISBN 10:
1-13311-087-8
ISBN 13:
978-1-13311-087-3
Chapter 3 - Determinants - 3.2 Determinants and Elementary Operations - 3.2 Exercises - Page 119: 45
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