Trigonometry (11th Edition) Clone

Published by Pearson
ISBN 10: 978-0-13-421743-7
ISBN 13: 978-0-13421-743-7

Chapter 5 - Trigonometric Identities - Section 5.3 Sum and Difference Identities for Cosine - 5.3 Exercises - Page 219: 57


$$\cos42^\circ=\cos(30^\circ+12^\circ)$$ 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.
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