Precalculus (6th Edition) Blitzer

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

Chapter 8 - Section 8.3 - Matrix Operations and Their Applications - Exercise Set - Page 920: 81

Answer

Matrix A is $A=\left[ \begin{matrix} 1 & 0 \\ 0 & 1 \\ \end{matrix} \right]$ and matrix B is $B=\left[ \begin{matrix} a & c \\ b & d \\ \end{matrix} \right]$.

Work Step by Step

Let, $A=\left[ \begin{matrix} 1 & 0 \\ 0 & 1 \\ \end{matrix} \right]$ And, $B=\left[ \begin{matrix} a & c \\ b & d \\ \end{matrix} \right]$ Then, the product operation on matrices is performed as shown below: $\begin{align} & AB=\left[ \begin{matrix} 1 & 0 \\ 0 & 1 \\ \end{matrix} \right]\left[ \begin{matrix} a & c \\ b & d \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 1\left( a \right)+0\left( b \right) & 1\left( c \right)+0\left( d \right) \\ 0\left( a \right)+1\left( b \right) & 0\left( c \right)+1\left( d \right) \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} a & c \\ b & d \\ \end{matrix} \right] \end{align}$ Then, $\begin{align} & BA=\left[ \begin{matrix} a & c \\ b & d \\ \end{matrix} \right]\left[ \begin{matrix} 1 & 0 \\ 0 & 1 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} a\left( 1 \right)+c\left( 0 \right) & a\left( 0 \right)+c\left( 1 \right) \\ b\left( 1 \right)+d\left( 0 \right) & b\left( 0 \right)+d\left( 1 \right) \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} a & c \\ b & d \\ \end{matrix} \right] \end{align}$ Therefore, the two matrices satisfy the condition $AB=BA$. Therefore, the required matrices are $A=\left[ \begin{matrix} 1 & 0 \\ 0 & 1 \\ \end{matrix} \right]$ and $B=\left[ \begin{matrix} a & c \\ b & d \\ \end{matrix} \right]$.
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