Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 7 - Trigonometric Identities and Equations - 7.3 Sum and Difference Identities - 7.3 Exercises: 39

Answer

$20^0$

Work Step by Step

$\cos \alpha =\sin \theta \Rightarrow \alpha +\theta =\dfrac {\pi }{2}\Rightarrow \sin \left( 3\theta -15\right) =\cos \left( \theta +25\right) \Rightarrow 3\theta -15+\theta +25=\dfrac {\pi }{2}=90\Rightarrow 4\theta +10=90\Rightarrow \theta =20^0$
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