Answer
$-\dfrac{2\sqrt{3}}{3}$
Work Step by Step
From problem 18 $\to \cos{\dfrac{A}{2}} =-\dfrac{\sqrt{3}}{2}$
$\because \sec{\dfrac{A}{2}} = \dfrac{1}{\cos{\dfrac{A}{2}}}$
$\therefore \sec{\dfrac{A}{2}} = \boxed{-\dfrac{2\sqrt{3}}{3}}$
Trigonometry 7th Edition
by McKeague, Charles P.; Turner, Mark D.
Published by
Cengage Learning
ISBN 10:
1111826854
ISBN 13:
978-1-11182-685-7
Chapter 5 - Section 5.4 - Half-Angle Formulas - 5.4 Problem Set - Page 304: 19
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