Answer
$ -1 $
Work Step by Step
$4cos^{-1}(x)-2\pi=2cos^{-1}(x) \Longrightarrow 2cos^{-1}(x)=2\pi \Longrightarrow cos^{-1}(x)=\pi \Longrightarrow x=cos(\pi)=-1 $
Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)
by Sullivan III, Michael
Published by
Pearson
ISBN 10:
0-32193-104-1
ISBN 13:
978-0-32193-104-7
Chapter 6 - Analytic Trigonometry - Section 6.1 The Inverse Sine, Cosine, and Tangent Functions - 6.1 Assess Your Understanding - Page 474: 67
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