Elementary Linear Algebra 7th Edition

Published by Cengage Learning
ISBN 10: 1-13311-087-8
ISBN 13: 978-1-13311-087-3

Chapter 2 - Matrices - 2.2 Properties of Matrix Operations - 2.2 Exercises - Page 60: 40

Answer

$(AB)^T=B^TA^T$.

Work Step by Step

Since we have $$AB=\left[\begin{array}{ccc}{1} &{2} \\ {0}& {-2} \end{array}\right]\left[\begin{array}{cc}{-3} &{-1} \\{2}& {1} \end{array}\right]=\left[\begin{array}{cc}{1} &{1} \\{-4}& {-2} \end{array}\right]$$ then $$(AB)^T=\left[\begin{array}{cc}{1} &{-4} \\{1}& {-2} \end{array}\right].$$ Now, $$B^TA^T= \left[\begin{array}{ccc}{-3} &{2} \\ {-1} &{1} \end{array}\right]\left[\begin{array}{ccc}{1} &{0} \\{2} & {-2} \end{array}\right]=\left[\begin{array}{cc}{1} &{-4} \\{1}& {-2} \end{array}\right].$$ It is easy to see that $(AB)^T=B^TA^T$.
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