Precalculus (6th Edition) Blitzer

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

Chapter 5 - Section 5.4 - Product-to-Sum and Sum-to-Product Formulas - Exercise Set - Page 690: 46

Answer

The graphs do not appear to coincide.
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Work Step by Step

Please note that the graphs of $y=\cos x +\cos 2x$ (the red graph) and $y=\cos 3x$ (the blue graph) do not coincide. For $x=\frac{\pi }{2}$ we have$$\cos \frac{\pi }{2} + \cos 2(\frac{\pi }{2})=-1 \neq 0 = \cos \frac{3\pi }{2}.$$
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