Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 6 - Trigonometric Functions - 6.3 Properties of the Trigonometric Functions - 6.3 Assess Your Understanding - Page 394: 20


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

Work Step by Step

$\sin \alpha =\sin \left( \alpha -2\pi k\right) \\\Rightarrow \sin \dfrac {9\pi }{4}=\sin \left( \dfrac {9\pi }{4}-2\pi \right) \\=\sin \dfrac {\pi }{4} \\=\dfrac {\sqrt {2}}{2}$
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