#### Answer

$\dfrac {\sqrt {10}}{10}$

#### Work Step by Step

$\cos \left( \arctan x\right) =\dfrac {1}{\sqrt {1+x^{2}}}\Rightarrow \cos \left( \arctan 3\right) =\dfrac {1}{\sqrt {1+3^2}}=\dfrac {\sqrt {10}}{10}$

Published by
Pearson

ISBN 10:
013421742X

ISBN 13:
978-0-13421-742-0

$\dfrac {\sqrt {10}}{10}$

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