Answer
$\dfrac{\sqrt{3}}{2}$
Work Step by Step
The cosine is an even function so
$\cos{(- \theta)} = \cos{\theta}$
Thus,
$\cos{(-30 ^{\circ})} = \cos{(30^{\circ})}= \boxed{\dfrac{\sqrt{3}}{2}}$
Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)
by Sullivan III, Michael
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
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