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 - 3.5 Chapter Review - Additional Problems - Page 244: 30

Answer

See below

Work Step by Step

Given: $A=\begin{bmatrix} 0 & 0 & 0 & 1\\0 & 1 & 3 & -3\\-2 & -3& -5&2\\4&-4&4&6 \end{bmatrix}$ We will use Cofactor Expansion Theorem to find the determinant of this matrix. $\det(A)=\sum^n_{j=1}a_{kj}C_{kj}\\ \det(A)=\sum^n_i=1 a_{ik}C_{ik}$ Then $\rightarrow \det(A)=-1\begin{vmatrix} 0&1&3\\-2& -3& -5\\ 4&-4&4 \end{vmatrix}\\ =-1[2(1.4-3.(-4))+4(1.(-5)-3.(-3))\\ =-48$ By using adjoint method, we have $A^{-1}=\frac{1}{\det(A)}adj(A)=\frac{1}{\det(A)}C^T$ where $C$ is cofactor matrix. Obtain: $adj(A)=\begin{bmatrix} 88&32&16&-4\\-24& 12&12 &6 \\-40&-20& -4 & -2\\-48 & 0 &0 &0 \end{bmatrix}$ Consequently, $A^{-1}=\frac{-1}{48}\begin{bmatrix} 88&32&16&-4\\-24& 12&12 &6 \\-40&-20& -4 & -2\\-48 & 0 &0 &0 \end{bmatrix}=\begin{bmatrix} \frac{-11}{6}& \frac{-2}{3}&\frac{-1}{3} &\frac{1}{12}\\\frac{1}{2}& \frac{-1}{4}& -\frac{1}{4} & -\frac{1}{8} \\\frac{5}{6}&\frac{5}{12}& \frac{1}{12} &\frac{1}{24} \\1 &0 & 0 &0 \end{bmatrix}$
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