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 - Page 487: 12

Answer

(d).

Work Step by Step

We can identify that it is the addition formula for a sine function. As $60+20=80$, the answer is (d).
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