Precalculus (6th Edition) Blitzer

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

Chapter 5 - Section 5.2 - Sum and Difference Formulas - Exercise Set - Page 671: 97


The given statement makes sense.

Work Step by Step

Once the formula for differences of cosines is verified, the other sum and difference formulas can be verified just by changing the values of angles. Let us take an example, $\cos \left( a-b \right)=\cos a\cos b+\sin a\sin b$ Replace b by -b: $\cos \left( a+b \right)=\cos a\cos b-\sin a\sin b$ Hence, verified.
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