Answer
$\dfrac{2}{\sqrt{x^2+4}}$
Work Step by Step
$\theta = \tan^{-1} \dfrac{x}{2}$
$\tan{\theta} =\dfrac{x}{2}$
$\sec{\theta} =\sqrt{1+\tan^2{\theta}} = \dfrac{\sqrt{x^2+4}}{2}$
$\cos{\theta} = \dfrac{2}{\sqrt{x^2+4}}$
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: 18
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