Precalculus (6th Edition)

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

Chapter 7 - Trigonometric Identities and Equations - 7.4 Double-Angle and Half-Angle Identities - 7.4 Exercises: 22

Answer

$\tan 30=\dfrac {\sqrt {3}}{3}$

Work Step by Step

$\dfrac {2\tan \alpha }{1-\tan ^{2}\alpha }=\tan _{2}\alpha \Rightarrow \dfrac {2\tan 15}{1-\tan ^{2}15}=\tan \left( 2\times 15\right) =\tan 30=\dfrac {\sqrt {3}}{3}$
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