Answer
$\dfrac{7}{9}$
Work Step by Step
$\alpha = \sin^{-1} {\dfrac{1}{3}}$
$\sin{\alpha} =\dfrac{1}{3}$
$\cos{2\alpha} = 1-2 \sin^2{\alpha} = \dfrac{7}{9}$
Trigonometry 7th Edition
by McKeague, Charles P.; Turner, Mark D.
Published by
Cengage Learning
ISBN 10:
1111826854
ISBN 13:
978-1-11182-685-7
Chapter 5 - Section 5.5 - Additional Identities - 5.5 Problem Set - Page 311: 14
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