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: 55

Answer

$x = 1.817-0.550~i$ $x = -1.817+0.550~i$

Work Step by Step

$x^2-3+2i = 0$ $x^2 = 3-2i$ We can find $r$: $r = \sqrt{(3)^2+(-2)^2} = \sqrt{13}$ Note that $~~3-2i~~$ is in the fourth quadrant: $tan~\theta = -\frac{2}{3}$ $\theta = tan^{-1}(-\frac{2}{3})$ $\theta = -33.69^{\circ}$ We can find $x$: When $k=0$: $x = (\sqrt{13})^{1/2}(cos~\frac{-33.69^{\circ}+360^{\circ}~k}{2}+i~sin~\frac{-33.69^{\circ}+360^{\circ}~k}{2})$ $x = (\sqrt{13})^{1/2}~[cos~(-16.85^{\circ})+i~sin~(-16.85^{\circ})]$ $x = 1.817-0.550~i$ When $k=1$: $x = (\sqrt{13})^{1/2}(cos~\frac{-33.69^{\circ}+360^{\circ}~k}{2}+i~sin~\frac{-33.69^{\circ}+360^{\circ}~k}{2})$ $x = (\sqrt{13})^{1/2}(cos~163.15^{\circ}+i~sin~163.15^{\circ})$ $x = -1.817+0.550~i$
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