Precalculus (6th Edition) Blitzer

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

Chapter 2 - Section 2.1 - Complex Numbers - Exercise Set - Page 315: 83

Answer

The value of the operation for the expression $\frac{8}{1+\frac{2}{i}}$ in the standard form is\[\frac{8}{5}+\frac{16}{5}i\]

Work Step by Step

Consider the expression, $\frac{8}{1+\frac{2}{i}}$ Multiply the expression $1$ by $\frac{i}{i}$ . $\begin{align} & \frac{8}{1+\frac{2}{i}}=\frac{8}{1\cdot \frac{i}{i}+\frac{2}{i}} \\ & =\frac{8}{\frac{i+2}{i}} \\ & =\frac{8}{\frac{i+2}{\frac{i}{1}}} \\ & =\frac{8}{i+2}\cdot \frac{i}{1} \end{align}$ Simplify it further as, $\begin{align} & \frac{8}{1+\frac{2}{i}}=\frac{8i}{i+2} \\ & =\frac{8i}{2+i} \end{align}$ Multiply the denominator term by its complex conjugate; that is, multiply the term $\frac{8i}{2+i}$ by $\frac{2-i}{2-i}$. $\begin{align} & \frac{8}{1+\frac{2}{i}}=\frac{8i}{i+2} \\ & =\frac{8i}{2+i}\cdot \frac{2-i}{2-i} \\ & =\frac{8i\left( 2-i \right)}{\left( 2-i \right)\left( 2+i \right)} \end{align}$ The product of a complex number $\left( a+bi \right)$ and its complex conjugate $\left( a-bi \right)$ results in a real number, that is $\left( a+bi \right)\left( a-bi \right)={{a}^{2}}+{{b}^{2}}$. Apply it, $\begin{align} & \frac{8}{1+\frac{2}{i}}=\frac{8i\left( 2-i \right)}{\left( 2-i \right)\left( 2+i \right)} \\ & =\frac{8i\left( 2-i \right)}{{{2}^{2}}+{{1}^{2}}} \\ & =\frac{8i\left( 2-i \right)}{4+1} \\ & =\frac{8i\left( 2-i \right)}{5} \end{align}$ The distributive property states that, $a\cdot \left( b+c \right)=a\cdot b+a\cdot c$. Apply it, $\begin{align} & \frac{8}{1+\frac{2}{i}}=\frac{8i\left( 2-i \right)}{5} \\ & =\frac{16i-8{{i}^{2}}}{5} \end{align}$ Recall that, $\begin{align} & \sqrt{-1}=i \\ & -1={{i}^{2}} \end{align}$ Apply it, $\begin{align} & \frac{8}{1+\frac{2}{i}}=\frac{8i\left( 2-i \right)}{5} \\ & =\frac{16i-8{{i}^{2}}}{5} \\ & =\frac{16i-8\left( -1 \right)}{5} \\ & =\frac{16i+8}{5} \end{align}$ Write it in the standard form $a+bi$. $\begin{align} & \frac{8}{1+\frac{2}{i}}=\frac{16i+8}{5} \\ & =\frac{8}{5}+\frac{16}{5}i \end{align}$ Thus, the value of the operation for the expression $\frac{8}{1+\frac{2}{i}}$ in the standard form is $\frac{8}{5}+\frac{16}{5}i$.
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