Answer
$-\frac{7}{8}$
Work Step by Step
1. $g(2\alpha)=cos(2\alpha)=2cos^2\alpha-1$
2. Use the given figures, we have $cos\alpha=-\frac{1}{4}, $
3. $g(2\alpha)=2(-\frac{1}{4})^2-1=-\frac{7}{8}$
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: 35
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