Precalculus (6th Edition)

by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie

Published by Pearson

ISBN 10: 013421742X

ISBN 13: 978-0-13421-742-0

Chapter 7 - Trigonometric Identities and Equations - 7.3 Sum and Difference Identities - 7.3 Exercises - Page 679: 19

Answer

$0$

Work Step by Step

$\cos 40\cos 50-\sin 40\sin 50=\cos \left( 40+50\right) =\cos 90=0$

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