Answer
$\frac{7}{25}$
Work Step by Step
1. Let $cos^{-1}\frac{4}{5}=t$, we have $cos(t)=\frac{4}{5}$
2. $cos(2cos^{-1}\frac{4}{5})=cos(2t)=2cos^2(t)-1=2(\frac{4}{5})^2-1=\frac{7}{25}$
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 - Section 6.6 Double-angle and Half-angle Formulas - 6.6 Assess Your Understanding - Page 519: 82
Update this answer!
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.
