Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 3 - Determinants - 3.3 Cofactor Expansions - True-False Review - Page 232: i

Answer

False

Work Step by Step

Let's analyse these matrixes to see whether the statement is true. $A=\begin{bmatrix} 1 & 2 \\ 3 & 4 \end{bmatrix}$ $B=\begin{bmatrix} 4 & 5 \\ 5 & 6 \end{bmatrix}$ $AB=\begin{bmatrix} 14 & 17 \\ 32 & 39 \end{bmatrix}$ $adj (AB)=\begin{bmatrix} 39 & -17 \\ -32 & 14 \end{bmatrix}$ $adj (A)=\begin{bmatrix} 4 & -2 \\ -3 & 1 \end{bmatrix}$ $adj (B)=\begin{bmatrix} 6 & -5 \\ -5 & 4 \end{bmatrix}$ $adj (A) adj (B)=\begin{bmatrix} 34 & -28 \\ -23 & 19 \end{bmatrix}$ It is clearly that: $adj (A) . adj (B) \ne adj (AB)$ Thus, the statement is false.
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