Trigonometry 7th Edition

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

Chapter 8 - Section 8.2 - Trigonometric Form for Complex Numbers - 8.2 Problem Set - Page 433: 59

Answer

The equivalent trigonometric form of $-11 + 2i$ is $5\sqrt{5}cis169.70^\circ$ or $5\sqrt{5}(cos169.70^\circ + isin169.70^\circ)$.

Work Step by Step

For $-11 + 2i$, the absolute value is $\sqrt{(-11)^2 + 2^2} = 5\sqrt{5}$ and $\theta = arctan(\frac{2}{-11}) = 169.70^\circ$, since $-11 + 2i$ is in the 2nd quadrant. Therefore, the equivalent trigonometric form of $-11 + 2i$ is $5\sqrt{5}cis169.70^\circ$ or $5\sqrt{5}(cos169.70^\circ + isin169.70^\circ)$.
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