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 213: 57

Answer

$$\cos42^\circ=\cos(30^\circ+12^\circ)$$ The statement is true.

Work Step by Step

$$\cos42^\circ=\cos(30^\circ+12^\circ)$$ Consider $\cos(30^\circ+12^\circ)$ As $30^\circ+12^\circ$ are put inside a parathesis, this means the sum must be carried out first. And since $30^\circ+12^\circ=42^\circ$, $$\cos(30^\circ+12^\circ)=\cos42^\circ$$ The statement is thus true.
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.