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: 46

Answer

$z=2\displaystyle \sqrt{2}(\cos\frac{\pi}{6}+i\sin\frac{\pi}{6})$

Work Step by Step

See p. 604, A complex number $z=a+bi$ has the polar (or trigonometric) form $z=r(\cos\theta+i\sin\theta)$ where $r=|z|=\sqrt{a^{2}+b^{2}}$ and $\tan\theta=b/a$. The number $r$ is the modulus of $z$, and $\theta$ is an argument of $z$. ------- $z=i(\sqrt{2}-\sqrt{6}i)=i\sqrt{2}-\sqrt{6}i^{2}=\sqrt{6}+i\sqrt{2}$ lies in Q.I. $r=|z|=\sqrt{(\sqrt{6})^{2}+(\sqrt{2})^{2}}=\sqrt{8}=2\sqrt{2}$ $\tan\theta =\displaystyle \frac{\sqrt{2}}{\sqrt{6}}=\frac{\sqrt{3}}{3}$ In Q.I,$\quad \displaystyle \tan(\frac{\pi}{6}) =\displaystyle \frac{\sqrt{3}}{3},$ So, $z=2\displaystyle \sqrt{2}(\cos\frac{\pi}{6}+i\sin\frac{\pi}{6})$
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