Trigonometry (10th Edition)

Published by Pearson
ISBN 10: 0321671775
ISBN 13: 978-0-32167-177-6

Chapter 8 - Complex Numbers, Polar Equations, and Parametric Equations - Section 8.4 De Moivre's Theorem: Powers and Roots of Complex Numbers - 8.4 Exercises - Page 378: 58

Answer

There are 64 complex roots. Two roots are real: $cos~0^{\circ}+i~sin~0^{\circ} = 1$ $cos~180^{\circ}+i~sin~180^{\circ} = -1$ 62 complex roots are not real.

Work Step by Step

$z = 1 = cos~0^{\circ}+i~sin~0^{\circ}$ $r = 1$ and $\theta = 0^{\circ}$ We can use this equation to find the 64th roots: $z^{1/n} = r^{1/n}~[cos(\frac{\theta}{n}+\frac{360^{\circ}~k}{n})+i~sin(\frac{\theta}{n}+\frac{360^{\circ}~k}{n})]$, where $k \in \{0, 1, 2,...,n-1\}$ Note that there are 64 complex roots. These two roots are real: $cos~0^{\circ}+i~sin~0^{\circ} = 1$ $cos~180^{\circ}+i~sin~180^{\circ} = -1$ All other 62 complex roots have a non-zero imaginary part. Thus, 62 complex roots are not real.
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