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 232: 14

Answer

$\det (A)=-52$

Work Step by Step

We have the cofactor expansion theorem is: $\det (A)=a_{11}C_{11}+a_{21}C_{21}+a_{31}C_{31}+a_{41}C_{41}$ with $C_{ij}=(-1)^{i+j}.M_{ij}$ to evaluate the given determinant of column 1: $\det (A)=-3.(-1)^{1+1}C_{11}+0.(-1)^{2+1}C_{21}+1.(-1)^{3+1}C_{31}+0.(-1)^{4+1}C_{41}$ $\det (A)=-3\begin{vmatrix} 4 &0 & 2 \\ 4 & -4 & 2 \\ 2 & 5 &0 \end{vmatrix}-0\begin{vmatrix} 0 &-1 & 0 \\ 4 & -4 & 2 \\ 2 & 5 &0 \end{vmatrix} +1\begin{vmatrix} 0 & -1 & 0 \\ 4 & 0 & 2 \\ 2 & 5 &0 \end{vmatrix}+0.\begin{vmatrix} 0 &-1 & 0 \\ 4 & 0 & 2 \\ 4 & -4 &2 \end{vmatrix}$ Plug in the given values: $\det (A)=-3(-40+56)+1(-4)$ $\det (A)=-48-4$ $\det (A)=-52$
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