Answer
$\frac{\sqrt 2}{2}$
Work Step by Step
Since $\frac{7\pi}{4}$ is in quadrant IV with a reference angle $\theta=2\pi-\frac{7\pi}{4}=\frac{\pi}{4}$, we have $cos(\frac{7\pi}{4})=cos(\frac{\pi}{4})=\frac{\sqrt 2}{2}$
Precalculus (6th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
Published by
Pearson
ISBN 10:
013421742X
ISBN 13:
978-0-13421-742-0
Chapter 6 - The Circular Functions and Their Graphs - Quiz - Page 616: 5
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