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 234: 60

Answer

$x_1=\frac{\det(B_1)}{\det(A)}=\frac{26}{11}$ $x_2=\frac{\det(B_2)}{\det(A)}=\frac{-3}{11}$

Work Step by Step

We are given: $x_1+5x_2=1$ $-3x_1+6x_2=-4$ which can also be written as: $A=\begin{bmatrix} 1 & 5\\ -3 & 6 \end{bmatrix} \rightarrow \det(A)=6+5=11$ $B_1=\begin{bmatrix} 1 & 5\\ -4 & 6 \end{bmatrix} \rightarrow \det(B_1)=6+20=26$ $B_2=\begin{bmatrix} 1 &1\\ -3 & -4 \end{bmatrix}\rightarrow \det(B_2)=-4+1=-3$ Use Cramer’s rule: $x_k=\frac{\det(B_k)}{\det(A)}$ to find the results: $x_1=\frac{\det(B_1)}{\det(A)}=\frac{26}{11}$ $x_2=\frac{\det(B_2)}{\det(A)}=\frac{-3}{11}$
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