Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

Published by Pearson
ISBN 10: 0-32193-104-1
ISBN 13: 978-0-32193-104-7

Chapter 5 - Trigonometric Functions - Section 5.3 Properties of the Trigonometric Functions - 5.3 Assess Your Understanding - Page 418: 60

Answer

$\dfrac{\sqrt{3}}{2}$

Work Step by Step

The cosine is an even function so $\cos{(- \theta)} = \cos{\theta}$ Thus, $\cos{(-30 ^{\circ})} = \cos{(30^{\circ})}= \boxed{\dfrac{\sqrt{3}}{2}}$
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