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 - Problems - Page 233: 21

Answer

$\det (A)=0$

Work Step by Step

We have the cofactor expansion theorem for the 1st row: $\det (A)=a_{11}C_{11}+a_{21}C_{21}+a_{31}C_{31}+a_{41}C_{41}$ with $C_{ij}=(-1)^{i+j}.M_{ij}$ So, we get: $\det (A)=2C_{11}+1C_{21}+0C_{31}+1C_{41}$ $\det (A)=2\begin{vmatrix} 4 & -2 & 3 \\ 2 & -1 & 0 \\ 3 & -2 & 4 \end{vmatrix}+1\begin{vmatrix} -1 & 3 & 1 \\ 2 & -1 & 0 \\ 0 & 0 & 1 \end{vmatrix}+(-1)\begin{vmatrix} -1 & 3 & 1 \\ 4 & -2 & 3 \\ 3 & -2 & 4 \end{vmatrix}+0\begin{vmatrix} -1 & 3 & 1 \\ 4 & -2 & 3 \\ 2 & -1 & 0 \end{vmatrix}$ Plug in the given values: $\det (A)=2[4.(-4)-2.(8+6)+3.3]+(-1)[1(-4+3)+4(1-6)]+0+(-1)[1(-4+4)-3(1-6)]$ $\det (A)=-6+21+0-15$ $\det (A)=0$
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