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 - Concept and Vocabulary Check - Page 917: 10

Answer

The statement is false.

Work Step by Step

Consider the following matrices: $A=\left[ \begin{matrix} 1 & 2 \\ 0 & 1 \\ \end{matrix} \right]$ And $B=\left[ \begin{matrix} 0 & 1 \\ 2 & 1 \\ \end{matrix} \right]$ Now calculate AB: $\begin{align} & AB=\left[ \begin{matrix} 1 & 2 \\ 0 & 1 \\ \end{matrix} \right]\left[ \begin{matrix} 0 & 1 \\ 2 & 1 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 0+4 & 1+2 \\ 0+2 & 0+1 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 4 & 3 \\ 2 & 1 \\ \end{matrix} \right] \end{align}$ And BA, $\begin{align} & BA=\left[ \begin{matrix} 0 & 1 \\ 2 & 1 \\ \end{matrix} \right]\left[ \begin{matrix} 1 & 2 \\ 0 & 1 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 0+0 & 1+0 \\ 2+0 & 4+1 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 0 & 1 \\ 2 & 5 \\ \end{matrix} \right] \end{align}$ Clearly, $AB\ne BA$ Hence, the statement is false.
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