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: 27

Answer

$\det(A)=2908$

Work Step by Step

$\det(A)=\begin{vmatrix} -3 & 2 & 0 & -1 & -4 \\ 1&3 &1&3&5 \\ 0& 2 & 1 &-3&-1 \\ 2 & 0 & 4 & -2 &-3 \\ -1 & 2 & 6 & 0 & -1 \end{vmatrix}=-\begin{vmatrix} 0 & 2 & 1 & -3 & -1 \\ 1&3 &1&3&5 \\ -3& 2 & 0 &-1&-4 \\ 2 & 0 & 4 & -2 &-3 \\ -1 & 2 & 6 & 0 & -1 \end{vmatrix}=-\begin{vmatrix} 0 & 2 & 1 & -3 & -1 \\ 1&3 &1&3&5 \\ 0& 11 & 3 &8&11 \\ 0 & -6 & 2 & -8 &-13 \\ 0 & 5& 7 & 3 & 4 \end{vmatrix}=-2\begin{vmatrix} 0 & 1 & \frac{1}{2} & -\frac{3}{2} & -\frac{1}{2} \\ 1&3 &1&3&5 \\ 0& 11& 3 &8&11 \\ 0 & -6 & 2 & -8 &-13 \\ 0 & 5 & 7 & 3 &4 \end{vmatrix}=-2\begin{vmatrix} 0 & 1 & \frac{1}{2} & -\frac{3}{2} & -\frac{1}{2} \\ 1&3 &1&3&5 \\ 0& 0& \frac{-5}{2} &\frac{-17}{2}&\frac{11}{2}\\ 0 & 0 & 5& -17 &-16 \\ 0 & 0 & \frac{9}{2} &\frac{21}{2} &\frac{13}{2} \end{vmatrix}=5\begin{vmatrix} 0 & 1 & \frac{1}{2} & -\frac{3}{2} & -\frac{1}{2} \\ 1&3 &1&3&5 \\ 0& 0& 1 &\frac{17}{5}&\frac{-11}{5} \\ 0 & 0 & 5 & -17 &-16 \\ 0 & 0 & \frac{9}{2} &\frac{21}{2} &\frac{13}{2} \end{vmatrix}=-170\begin{vmatrix} 0 & 1 & \frac{1}{2} & -\frac{3}{2} & -\frac{1}{2} \\ 1&3 &1&3&5 \\ 0& 0& 1 &\frac{17}{5}&\frac{-11}{5} \\ 0 & 0 & 0 & 1 &\frac{5}{34} \\ 0 & 0 &0 &\frac{-24}{5} &\frac{82}{5} \end{vmatrix}=-170\begin{vmatrix} 0 & 1 & \frac{1}{2} & -\frac{3}{2} & -\frac{1}{2} \\ 1&3 &1&3&5 \\ 0& 0& 1 &\frac{17}{5}&\frac{-11}{5} \\ 0 & 0 & 0 & 1 &\frac{5}{34} \\ 0 & 0 &0 &0 &\frac{1454}{85} \end{vmatrix}=170\begin{vmatrix} 1 & 3 &1 & 3 & 5 \\ 0&1 &\frac{1}{2}&\frac{-3}{2}&\frac{-1}{2} \\ 0& 0& 1 &\frac{17}{5}&\frac{-11}{5} \\ 0 & 0 & 0 & 1 &\frac{5}{34} \\ 0 & 0 &0 &0 &\frac{2908}{170} \end{vmatrix}$ We will apply Corollary 3.2.6. The determinant of the matrix of coefficients of the system is: $\det(A)=a_{11}C_{11}+a_{21}C_{21}+a_{31}C_{31}$ where $C_{ij}=(_1)^{i+j}.M_{ij}$ $\det (A)=170.[1(-1)^{1+1}.1.1.\frac{2908}{170}]$ $\det (A)=170.\frac{2908}{170}$ $\det(A)=2908$
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