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: 14

Answer

$\dfrac {\sqrt {2}}{4}\left( 1+\sqrt {3}\right) $

Work Step by Step

$\cos \left( 105\right) =\cos \left( 60+45\right) =\cos 60\cos 45+\sin 60\sin 45=\dfrac {\sqrt {2}}{4}\left( 1+\sqrt {3}\right) $
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