Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 13 - The Trigonometric Functions - 13.1 Definitions of the Trigonometric Functions - 13.1 Exercises - Page 678: 48


$\cos \frac{-\pi}{6}=\frac{-\sqrt 3}{2}$

Work Step by Step

We are given $\cos \frac{-\pi}{6}$ $\cos \frac{-\pi}{6}=\cos \frac{\pi}{6}$ convert $\frac{\pi}{6}$ radians to degrees $\frac{\pi}{6}=\frac{\pi}{6}(\frac{180^\circ}{\pi})$ $\frac{\pi}{6}=30^\circ$ $\cos \frac{\pi}{6}=(\cos 30^\circ)$ $\cos \frac{-\pi}{6}=-(\cos 30^\circ)$ $\cos 30^\circ=\frac{\sqrt 3}{2}$ so $\cos \frac{-\pi}{6}=\frac{-\sqrt 3}{2}$
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