Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 8 - Section 8.3 - Polar Form of Complex Numbers; De Moivre's Theorem - 8.3 Exercises - Page 611: 89

Answer

$z_0=2(cos~\frac{\pi}{18}+i~sin~\frac{\pi}{18})$ $z_1=2(cos~\frac{13\pi}{18}+i~sin~\frac{13\pi}{18})$ $z_2=2(cos~\frac{25\pi}{18}+i~sin~\frac{15\pi}{18})$

Work Step by Step

$z^3-4\sqrt 3-4i=0$ $z^3=4\sqrt 3+4i$ Polar form of $4\sqrt 3+4i$: $r=|z|=\sqrt {a^2+b^2}=\sqrt {(4\sqrt 3)^2+4^2}=\sqrt {64}=8$ $tan~θ=\frac{b}{a}=\frac{4}{4\sqrt 3}=\frac{\sqrt 3}{3}$ $θ=\frac{\pi}{6}$ $4\sqrt 3+4i=8(cos~\frac{\pi}{6}+i~sin~\frac{\pi}{6})$ $z_k=\sqrt[3]{8}[cos(\frac{\frac{\pi}{6}+2k\pi}{3})+i~sin(\frac{\frac{\pi}{6}+2k\pi}{3})]$ $z_0=2(cos~\frac{\pi}{18}+i~sin~\frac{\pi}{18})$ $z_1=2(cos~\frac{13\pi}{18}+i~sin~\frac{13\pi}{18})$ $z_2=2(cos~\frac{25\pi}{18}+i~sin~\frac{15\pi}{18})$
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