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 - Page 679: 30


$\cos \left( -\dfrac {\pi }{6}\right) $

Work Step by Step

$\alpha +\beta =\dfrac {\pi }{2}\Rightarrow \sin \alpha =\cos \beta \Rightarrow \dfrac {2\pi }{3}+\left( -\dfrac {\pi }{6}\right) =\dfrac {\pi }{2}\Rightarrow $ $\sin \left( \dfrac {2\pi }{3}\right) =\cos \left( -\dfrac {\pi }{6}\right) $
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