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: 49

Answer

$z_{1}z_{2}=6\left(\displaystyle \cos\frac{\pi}{2}+i\sin\frac{\pi}{2}\right)$ $\displaystyle \frac{z_{1}}{z_{2}}=\frac{3}{2}\left(\cos\frac{\pi}{6}+i\sin\frac{\pi}{6}\right)$

Work Step by Step

If two complex numbers $z_{1}$ and $z_{2}$ have the polar forms $z_{1}=r_{1}(\cos\theta_{1}+i\sin\theta_{1})$, $z_{2}=r_{2}(\cos\theta_{2}+i\sin\theta_{2})$, then their product and quotient can be written: $z_{1}z_{2}=r_{1}r_{2}[\cos(\theta_{1}+\theta_{2})+i\sin(\theta_{1}+\theta_{2})]$ $\displaystyle \frac{z_{1}}{z_{2}}=\frac{r_{1}}{r_{2}}[\cos(\theta_{1}-\theta_{2})+i\sin(\theta_{1}-\theta_{2})],\quad z_{2}\neq 0$ ---------- In our case we have: $r_1=3$, $r_2=2$ $\theta_1=\frac{\pi}{3}$, $\theta_2=\frac{\pi}{6}$ $r_{1}r_{2}= 3\displaystyle \cdot 2=6\qquad \frac{r_{1}}{r_{2}}=\frac{3}{2}$ $\theta_1+\theta_2=\displaystyle \frac{\pi}{3}+\frac{\pi}{6}=\frac{(2+1)\pi}{6}=\frac{\pi}{2}$, $\theta_1-\theta_2=\frac{\pi}{3}-\frac{\pi}{6}=\frac{(2-1)\pi}{6}=\frac{\pi}{6}$ $z_{1}z_{2}=6\left(\displaystyle \cos\frac{\pi}{2}+i\sin\frac{\pi}{2}\right)$ $\displaystyle \frac{z_{1}}{z_{2}}=\frac{3}{2}\left(\cos\frac{\pi}{6}+i\sin\frac{\pi}{6}\right)$
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