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 $
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 - 7.1 Fundamental Identities - 7.1 Exercises - Page 659: 72
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