Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 7 - Analytic Trigonometry - 7.5 Sum and Difference Formulas - 7.5 Assess Your Understanding: 2

Answer

$-\frac{3}{5}$

Work Step by Step

The identity says: $sin^2(\theta)+cos^2(\theta)=1$. Hence $cos(\theta)=\pm\frac{3}{5}$, but it is in quadrant II, hence $cos(\theta)=-\frac{3}{5}$
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