University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 1 - Section 1.3 - Trigonometric Functions - Exercises - Page 28: 39


$$\cos(\pi+x)=-\cos x$$

Work Step by Step

$$\cos(\pi+x)$$ Apply the addition formula for cosine: $$\cos(\pi+x)=\cos\pi\cos x-\sin\pi\sin x$$ $$\cos(\pi+x)=(-1)\times\cos x-0\times\sin x$$ $$\cos(\pi+x)=-\cos x$$
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