Answer
$-1$
Work Step by Step
Using the given identities: $\frac{\cos^2x\tan^2(-x)-1}{\cos^2x}=\frac{\cos^2x\tan^2x-1}{\cos^2x}=\frac{\cos^2x\frac{\sin^2x}{\cos^2x}-1}{\cos^2x}=\frac{\sin^2x-1}{\cos^2x}=\frac{-\cos^2x}{\cos^2x}=-1$
Algebra 2 (1st Edition)
by Larson, Ron; Boswell, Laurie; Kanold, Timothy D.; Stiff, Lee
Published by
McDougal Littell
ISBN 10:
0618595414
ISBN 13:
978-0-61859-541-9
Chapter 14 Trigonometric Graphs, Identities, and Equations - 14.3 Verify Trigonometric Identities - 14.3 Exercises - Skill Practice - Page 928: 21
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