Answer
$ 0$
Work Step by Step
$2cos^{-1}(x)+\pi=4cos^{-1}(x)\Longrightarrow cos^{-1}(x)=\frac{\pi}{2}$, thus $x=0$
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 - Chapter Review - Review Exercises - Page 528: 85
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