Answer
$\dfrac {\sqrt {10}}{10}$
Work Step by Step
$\cos \left( \arctan x\right) =\dfrac {1}{\sqrt {1+x^{2}}}\Rightarrow \cos \left( \arctan 3\right) =\dfrac {1}{\sqrt {1+3^2}}=\dfrac {\sqrt {10}}{10}$
Precalculus (6th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
Published by
Pearson
ISBN 10:
013421742X
ISBN 13:
978-0-13421-742-0
Chapter 7 - Trigonometric Identities and Equations - Chapter 7 Test Prep - Review Exercises - Page 738: 100
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