Trigonometry (11th Edition) Clone

Published by Pearson
ISBN 10: 978-0-13-421743-7
ISBN 13: 978-0-13421-743-7

Chapter 3 - Radian Measure and the Unit Circle - Section 3.1 Radian Measure - 3.1 Exercises - Page 105: 79



Work Step by Step

Convert the angle measure to degrees to obtain: $=3\pi \cdot \frac{180^o}{\pi} = 540^o$ Thus, $\cos{3\pi} = \cos{540^o}$ 540 degrees is on the negative x-axis and is coterminal with $540^o-360^o=180^o$. From Section 1.3 (page 25) , we learned that: $\cos{180^o} = -1$ This means that: $\cos{540^o} = \cos{180^o} = -1$
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