Trigonometry 7th Edition

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

Chapter 8 - Section 8.4 - Roots of a Complex Number - 8.4 Problem Set - Page 447: 20

Answer

The three cube roots are: \[ \begin{array}{l} [\cos 101+i \sin 101] 3\\ [\cos 221+i \sin 221] 3\\ [\cos 341+i \sin 341]3 \end{array} \]

Work Step by Step

\[ \left(\cos 303^{\circ}+i \sin 303^{\circ}\right)27 \] Using the roots theorem: \[ \left[\cos \left(\frac{\theta}{n}+\frac{360^{\circ}}{n} k\right)+i \sin \left(\frac{\theta}{n}+\frac{360^{\circ}}{n} k\right)\right]r^{\frac{1}{n}}=w_{k} \] When $0=k$ : \[ \left[\cos \left(\frac{303^{\circ}}{3}+\frac{360^{\circ}}{3}(0)\right)+i \sin \left(\frac{303^{\circ}}{3}+\frac{360^{\circ}}{3}(0)\right)\right]27^{\frac{1}{3}}=w_{0} \] Simplify: \[ =\sqrt{3 \cos 101^{\circ}+i \sin 101^{\circ}} \] When $1=k$ : \[ \left[\cos \left(\frac{303^{\circ}}{3}+\frac{360^{\circ}}{3}(1)\right)+i \sin \left(\frac{303^{\circ}}{3}+\frac{360^{\circ}}{3}(1)\right)\right]27^{\frac{1}{3}}=w_{1} \] Simplify: \[ \begin{array}{r} =\left[\cos \left(101^{\circ}+120^{\circ}\right)+i \sin \left(101^{\circ}+120^{\circ}\right)\right]3 \\ =\left[3\left[\cos 221^{\circ}+i \sin 221^{\circ}\right]\right. \end{array} \] When $2=k$ : \[ \left[\cos \left(\frac{303^{\circ}}{3}+\frac{360^{\circ}}{3}(2)\right)+i \sin \left(\frac{303^{\circ}}{3}+\frac{360^{\circ}}{3}(2)\right)\right]27^{\frac{1}{3}}=w_{2} \] Simplify: \[ \begin{array}{r} =\left[\cos \left(101^{\circ}+240^{\circ}\right)+i \sin \left(101^{\circ}+240^{\circ}\right)\right] \\ =\left[\cos 341^{\circ}+i \sin 341^{\circ}\right]3 \end{array} \]
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.