Answer
$\tan 30=\dfrac {\sqrt {3}}{3}$
Work Step by Step
$\dfrac {2\tan \alpha }{1-\tan ^{2}\alpha }=\tan _{2}\alpha \Rightarrow \dfrac {2\tan 15}{1-\tan ^{2}15}=\tan \left( 2\times 15\right) =\tan 30=\dfrac {\sqrt {3}}{3}$
Precalculus (6th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
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 - Page 693: 22
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