Trigonometry 7th Edition

Published by Cengage Learning
ISBN 10: 1111826854
ISBN 13: 978-1-11182-685-7

Chapter 5 - Section 5.2 - Sum and Difference Formulas - 5.2 Problem Set - Page 289: 33

Answer

$\cos{90}=0 $

Work Step by Step

$\cos{(A+B)} = \cos{A} \cos{B} - \sin{A} \sin{B}$ $\cos{(15)} \cos{(75)} - \sin{(15)} \sin{(75)} = \cos{(15+75)} = \cos{90}=0 $
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