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 - Page 694: 67


$\sin 20$

Work Step by Step

$\sqrt {\dfrac {1-\cos 40}{2}}=\sqrt {\dfrac {1-\cos \left( 2\times 20\right) }{2}}=\sqrt {\dfrac {1-\left( \cos ^{2}20-\sin ^{2}20\right) }{2}}=\sqrt {\dfrac {2\sin ^{2}20}{2}}=\sin 20$
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