Answer
$$\cos(\pi+x)=-\cos x$$
Work Step by Step
$$\cos(\pi+x)$$
Apply the addition formula for cosine:
$$\cos(\pi+x)=\cos\pi\cos x-\sin\pi\sin x$$
$$\cos(\pi+x)=(-1)\times\cos x-0\times\sin x$$
$$\cos(\pi+x)=-\cos x$$
University Calculus: Early Transcendentals (3rd Edition)
by Hass, Joel R.; Weir, Maurice D.; Thomas Jr., George B.
Published by
Pearson
ISBN 10:
0321999584
ISBN 13:
978-0-32199-958-0
Chapter 1 - Section 1.3 - Trigonometric Functions - Exercises - Page 28: 39
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