#### Answer

$-\sin ^{2}\theta $

#### Work Step by Step

$\cos \theta \left( \cos \theta -sec\theta \right) =\cos \theta \left( \cos \theta -\dfrac {1}{\cos \theta }\right) =\cos ^{2}\theta -1=-\sin ^{2}\theta $

Published by
Pearson

ISBN 10:
013421742X

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

$-\sin ^{2}\theta $

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