Answer
$-\frac{7}{9}$
Work Step by Step
$\cos 2A=2\cos^{2}A-1$
$=2(\cos A)^{2}-1$
$=2(-\frac{1}{3})^{2}-1$
$=2(\frac{1}{9})-1=-\frac{7}{9}$
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 8 - Section 8.3 - Products and Quotients in Trigonometric Form - 8.3 Problem Set - Page 440: 65
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