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 610: 66

Answer

$-32i$

Work Step by Step

See p. 606, If $z=r(\cos\theta+i\sin\theta)$, then for any integer $n$ $z^{n}=r^{n}(\cos n\theta+i\sin n\theta)$ ----------- $z=1-i$ $\theta$ terminates in quadrant IV, $\displaystyle \tan\theta=\frac{-1}{1}=-1$ $\Rightarrow \displaystyle \theta=\frac{7\pi}{4}$, $r=\sqrt{1+1}=\sqrt{2}$ $z=\displaystyle \sqrt{2}(\cos\frac{7\pi}{4}+i\sin\frac{7\pi}{4})$ $z^{10}=(2^{1/2})^{10}[\displaystyle \cos(10\cdot\frac{7\pi}{4})+i\sin(10\cdot\frac{7\pi}{4})]$ $=2^{5}(\displaystyle \cos\frac{35\pi}{2}+i\sin\frac{35\pi}{2})$ With $\displaystyle \cos\frac{35\pi}{2}=0,$ $\displaystyle \sin\frac{35\pi}{2}=\sin(\frac{3\pi}{2}+16\pi)=-1$, $z^{10}=32(0-i)=-32i$
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