Elementary Linear Algebra 7th Edition

Published by Cengage Learning
ISBN 10: 1-13311-087-8
ISBN 13: 978-1-13311-087-3

Chapter 3 - Determinants - 3.4 Applications of Determinants - 3.4 Exercises - Page 136: 20

Answer

The system can be solved by using Cramer's Rule: $x_1=1/2$ and $x_2=1/3$

Work Step by Step

The coefficient matrix is $A=\left[\begin{array}{cc} 18&12\\ 30&24 \end{array}\right]$ and $|A|=18*24-360=72\ne 0$. Then $A$ is anonsingular matrix Thus the linear system can be solved by using Cramer's Rule. Therefore the system has the unique solution: $x_1=|A_1|/|A|$ and $x_2=|A_2|/|A|$ where, $A_1=\left[\begin{array}{cc} 13&12\\ 23&24 \end{array}\right]$ $A_2=\left[\begin{array}{cc} 18&13\\ 30&23 \end{array}\right]$ $|A_1=13*24-12*23=36$ $|A_2|=18*23-30*13=24$ $x_1=|A_1|/|A|=36/72=1/2$ and $x_2=|A_2|/|A|=24/72=1/3$
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