#### Answer

$=\cos 4x$

#### Work Step by Step

$\cos ^{2}\alpha -\sin ^{2}\alpha =\cos ^{2}\alpha \Rightarrow \cos ^{2}2x-\sin ^{2}2x=\cos \left( 2\times 2x\right) =\cos 4x$

Published by
Pearson

ISBN 10:
013421742X

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

$=\cos 4x$

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