Answer
$2$
Work Step by Step
$\sec{(\theta+ 360^{\circ} k)} = \sec{\theta}$
$\therefore \sec{420^{\circ}} = \sec{(60^{\circ}+360^{\circ})} = \sec{60^{\circ}}$
$\sec{60^{\circ}} = \dfrac{1}{\cos{60^{\circ}}}=\dfrac{1}{\frac{1}{2}}=\boxed{2}$
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 417: 18
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