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: 13

Answer

$\det (A)=72$

Work Step by Step

We have the cofactor expansion theorem is: $\det (A)=a_{14}C_{14}+a_{24}C_{24}+a_{34}C_{34}+a_{44}C_{44}$ with $C_{ij}=(-1)^{i+j}.M_{ij}$ to evaluate the given determinant of column 1: $\det (A)=0.(-1)^{1+4}C_{14}-2.(-1)^{2+4}C_{24}+4.(-1)^{3+4}C_{34}+0.(-1)^{4+4}C_{44}$ $\det (A)=0-2\begin{vmatrix} 1 & -2 & 3 \\ 0 & 1 & 3 \\ 1 & 5 & -2 \end{vmatrix} -4\begin{vmatrix}1 & -2 & 3 \\ 4 & 0 &7 \\ 1 & 5 & -2 \end{vmatrix}+0$ Plug in the given values: $\det (A)=-2(-17-0-9)-4(-30+25)$ $\det (A)=52+20$ $\det (A)=72$
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