Intermediate Algebra: Connecting Concepts through Application

Published by Brooks Cole
ISBN 10: 0-53449-636-9
ISBN 13: 978-0-53449-636-4

Chapter 8 - Radical Functions - 8.5 Complex Numbers - 8.5 Exercises - Page 663: 65

Answer

$-\frac{29}{85}+\frac{82}{85} i $

Work Step by Step

Rewrite the given expression, and solve the latter. \begin{equation} \frac{-8-5 i}{-2+9 i}= (-1)\cdot \frac{-8-5i}{2-9i} = \frac{8+5i}{2-9i}. \end{equation} Multiply both numerator and denominator by the conjugate of the denominator and simplify. \begin{equation} \begin{aligned} \frac{8+5i}{2-9i}&=\frac{8+5i}{2-9i}\cdot \frac{(2+9i)}{(2+9i)}\\ & =\frac{8(2+9i)+5i(2+9i)}{4+81}\\ &=\frac{16+72i+10i-45}{85}\\ &= -\frac{29}{85}+\frac{82}{85} i. \end{aligned} \end{equation}
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