Answer
$\dfrac{\sqrt{2+\sqrt{3}}}{2}$
Work Step by Step
$\cos{\dfrac{A}{2}} = \sqrt{\dfrac{1+\cos{A}}{2}}$
$\cos{15} =\sqrt{\dfrac{1+\cos{30}}{2}} = \sqrt{\dfrac{1+\dfrac{\sqrt{3}}{2}}{2}}$
$\cos{15} = \dfrac{\sqrt{2+\sqrt{3}}}{2}$
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 305: 39
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