Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 7 - Trigonometric Identities and Equations - 7.3 Sum and Difference Identities - 7.3 Exercises - Page 680: 66



Work Step by Step

Use the subtraction formula for cosine, $\cos (A+B)=\cos A\cos B-\sin A\sin B$: $\cos(270^\circ+\theta)$ $=\cos 270^\circ\cos \theta-\sin 270^\circ\sin \theta$ $=0*\cos\theta-(-1)*\sin\theta$ $=\sin\theta$
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