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: 83

Answer

The matrices A and B are anti commutative.

Work Step by Step

Calculate $AB$: $\begin{align} & AB=\left[ \begin{matrix} 0 & -1 \\ 1 & 0 \\ \end{matrix} \right]\left[ \begin{matrix} 1 & 0 \\ 0 & -1 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 0\left( 1 \right)-1\left( 0 \right) & 0\left( 0 \right)-1\left( -1 \right) \\ 1\left( 1 \right)+0\left( 0 \right) & 1\left( 0 \right)+0\left( -1 \right) \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 0 & 1 \\ 1 & 0 \\ \end{matrix} \right] \end{align}$ Calculate $-BA$: $\begin{align} & -BA=-\left[ \begin{matrix} 1 & 0 \\ 0 & -1 \\ \end{matrix} \right]\left[ \begin{matrix} 0 & -1 \\ 1 & 0 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} -1 & 0 \\ 0 & 1 \\ \end{matrix} \right]\left[ \begin{matrix} 0 & -1 \\ 1 & 0 \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} -1\left( 0 \right)+0\left( 1 \right) & -1\left( -1 \right)+0\left( 0 \right) \\ 0\left( 0 \right)+1\left( 1 \right) & 0\left( -1 \right)+1\left( 0 \right) \\ \end{matrix} \right] \\ & =\left[ \begin{matrix} 0 & 1 \\ 1 & 0 \\ \end{matrix} \right] \end{align}$ It can be clearly seen that $AB=-BA$. Hence, the matrices A and B are anti-commutative.
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