Answer
$\dfrac{4}{5}$
Work Step by Step
$\alpha = \cos^{-1} {\dfrac{\sqrt{5}}{5}}$
$\cos{\alpha}=\dfrac{\sqrt{5}}{5}$
$\sin{\alpha} = \sqrt{1-\cos^2{\alpha}} = \dfrac{2\sqrt{5}}{5}$
$\sin{2\alpha} = 2 \sin{\alpha} \cos{\alpha} = \dfrac{4}{5}$
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: 11
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