Trigonometry 7th Edition

Published by Cengage Learning
ISBN 10: 1111826854
ISBN 13: 978-1-11182-685-7

Chapter 8 - Section 8.3 - Products and Quotients in Trigonometric Form - 8.3 Problem Set - Page 440: 63

Answer

$\frac{\sqrt 3}{4}+\frac{1}{4}i$

Work Step by Step

$\sqrt {3}-i$ in trigonometric form is $2(\cos 330^{\circ}+i\sin 330^{\circ})$ We use de Moivre's theorem to find its reciprocal. $(\sqrt {3}-i)^{-1}=[2(\cos330^{\circ}+i\sin330^{\circ})]^{-1}$ $=(2)^{-1}[\cos(-1\cdot 330^{\circ})+i\sin(-1\cdot330^{\circ})]$ $=\frac{1}{2}(\cos -330^{\circ}+i\sin-330^{\circ})$ $=\frac{1}{2}(\cos 30^{\circ}+i\sin30^{\circ})$ ($30^{\circ}$ and $-330^{\circ}$ are coterminal.) In standard form, our result is $\frac{1}{2}(\frac{\sqrt {3}}{2}+i\cdot \frac{1}{2})=\frac{\sqrt 3}{4}+\frac{1}{4}i$
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