Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 6 - Section 6.5 - Complex Numbers in Polar Form; DeMoivre's Theorem - Exercise Set - Page 768: 63

Answer

The power of the complex numbers in the rectangular form is $-64$.

Work Step by Step

Consider the given complex number to write in the polar form, $z={{\left( \sqrt{3}-i \right)}^{6}}$ ...... (1) For a complex number $z=x+iy$, the polar form is given by, $z=r\left( \cos \theta +i\sin \theta \right)$ ...... (2) Here, $x=r\cos \theta \ \text{ and }\ y=r\sin \theta $, dividing the value of y by x, to get, $\tan \theta =\frac{y}{x}$ ...... (3) Also, the value of r is called the moduli of the complex number, given by, $\begin{align} & r=\sqrt{{{x}^{2}}+{{y}^{2}}} \\ & =\sqrt{{{\left( \sqrt{3} \right)}^{2}}+{{\left( -1 \right)}^{2}}} \\ & =\sqrt{3+1} \\ & =2 \end{align}$ For any complex number $z=x+iy$, the sign of the value of x and y determine in which quadrant the value of $z=x+iy$ would lie. If the value of x lies on the positive side and the value of y is positive, then the angle $\theta $ lies in the first quadrant having the value of $\theta $ as $\theta $. If the value of x lies on the negative side and the value of y is positive, then the angle $\theta $ lies in the second quadrant having the value of $\theta $ as $\pi -\theta $. If the value of x lies on the negative side and the value of y is negative, then the angle $\theta $ lies in the third quadrant having the value of $\theta $ as $\pi +\theta $. If the value of x lies on the positive side and the value of y is negative, then the angle $\theta $ lies in the fourth quadrant having the value of $\theta $ as $2\pi -\theta $. For the given complex number, using (1), (3) to get, $\tan \theta =\frac{y}{x}=\frac{-1}{\sqrt{3}}=-\frac{1}{\sqrt{3}}$ For the given complex number, $\theta =\frac{11\pi }{6}$ Use (2), to get, $\left( \sqrt{3}-i \right)=2\left( \cos \frac{11\pi }{6}+i\sin \frac{11\pi }{6} \right)$ The polar form of the complex number is, $z={{\left[ 2\left( \cos \frac{11\pi }{6}+i\sin \frac{11\pi }{6} \right) \right]}^{6}}$ Consider the given complex number in the polar form, $z={{\left[ 2\left( \cos \frac{11\pi }{6}+i\sin \frac{11\pi }{6} \right) \right]}^{6}}$ ...... (4) If n is a positive integer, then ${{z}^{n}}$ is, $\begin{align} & {{z}^{n}}={{\left[ r\left( \cos \theta +i\sin \theta \right) \right]}^{n}} \\ & ={{r}^{n}}\left( \cos n\theta +i\sin n\theta \right) \end{align}$ That is., ${{z}^{n}}={{r}^{n}}\left( \cos n\theta +i\sin n\theta \right)$ Now, for the given complex number, use (4) to get, $\begin{align} & z={{\left[ 2\left( \cos \frac{11\pi }{6}+i\sin \frac{11\pi }{6} \right) \right]}^{6}} \\ & z={{2}^{6}}\left( \cos 6\times \frac{11\pi }{6}+i\sin 6\times \frac{11\pi }{6} \right) \\ & z=64\left( \cos 11\pi +i\sin 11\pi \right) \\ \end{align}$ Simplifying it further, to get, $\begin{align} & z=64\left( -1+i0 \right) \\ & z=-64 \\ \end{align}$ The power of the complex numbers in the rectangular form is $-64$.
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.