Trigonometry (10th Edition)

Published by Pearson
ISBN 10: 0321671775
ISBN 13: 978-0-32167-177-6

Chapter 5 - Trigonometric Identities - Section 5.3 Sum and Difference Identities for Cosine - 5.3 Exercises - Page 212: 2

Answer

2 is matched with A to have an identity.

Work Step by Step

According to the given identity, we have that $$\cos(x-y)=\cos x\cos y+\sin x\sin y$$ Now we match with the expressions in II. We find that the second expression in I matches the expression A in II. Therefore, we would match 2 with A to have an identity.
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