Answer
$-\frac{7}{25}$
Work Step by Step
1. Let $tan^{-1}(\frac{4}{3})=t$ (t in quadrant I), we have $tan(t)=\frac{4}{3}$ and $sin(t)=\frac{4}{5}$
2. Thus $cos(2t)=1-2sin^2(t)=1-2(\frac{4}{5})^2=-\frac{7}{25}$
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: 63
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