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: 61

Answer

$x_1=\frac{-11}{27}$ $x_2=\frac{-35}{27}$ $x_3=\frac{-17}{27}$

Work Step by Step

We are given: $x_1+5x_2=1$ $-3x_1+6x_2=-4$ which can also be written as: $A=\begin{bmatrix} -2 & 4&1\\ 3 & -2&-1\\ 4&-3&-2 \end{bmatrix} \rightarrow \det(A)=14-40-1=-27$ $B_1=\begin{bmatrix} -5 & 4&1\\ 2 & -2&-1\\ 1&-3&-2 \end{bmatrix} \rightarrow \det(A)=35-20-4=11$ $B_2=\begin{bmatrix} -2 &-5&1\\ 3 & 2&-1\\ 4&1&2 \end{bmatrix} \rightarrow \det(A)=-10+50-5=35$ $B_3=\begin{bmatrix} -2 &4&-5\\ 3 & -2&2\\ 4&-3&1 \end{bmatrix} \rightarrow \det(A)=-8+20+5=17$ Use Cramer’s rule: $x_k=\frac{\det(B_k)}{\det(A)}$ to find the results: $x_1=\frac{\det(B_1)}{\det(A)}=\frac{-11}{27}$ $x_2=\frac{\det(B_2)}{\det(A)}=\frac{-35}{27}$ $x_3=\frac{\det(B_3)}{\det(A)}=\frac{-17}{27}$
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