Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 5 - Review Exercises - Page 708: 46


$\frac{\sqrt 6}{2}$

Work Step by Step

Using the Sum-to-Product Formula $cos(u)+cos(v)=2cos\frac{u+v}{2}cos\frac{u-v}{2}$, we have $cos(75^\circ )+cos(15^\circ)=2cos\frac{75^\circ+15^\circ}{2}cos\frac{75^\circ-15^\circ}{2}=2cos(45^\circ) cos(30^\circ)=2(\frac{\sqrt 2}{2})(\frac{\sqrt 3}{2})=\frac{\sqrt 6}{2}$
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