#### Answer

$\left( 1+\cos ^{2}x\right) ^{2}$

#### Work Step by Step

$\cos ^{4}x+2\cos ^{2}x+1=\left( \cos ^{2}x\right) ^{2}+2\times 1\times \cos ^{2}x+1^{2}=\left( 1+\cos ^{2}x\right) ^{2}$

Published by
Pearson

ISBN 10:
013421742X

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

$\left( 1+\cos ^{2}x\right) ^{2}$

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