College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter 8 - Section 8.4 - Matrix Algebra - 8.4 Assess Your Understanding - Page 598: 59

Answer

$x=1/3, \ y=1, \ z=2/3$ or $(1/3, \ 1, \ 2/3)$

Work Step by Step

Writing the system in matrix form, $AX=B,$ the solution is $X=A^{-1}B$. Here, $A=\left[\begin{array}{lll}{1}&{1}&{1}\\{3}&{2}&{-1}\\{3}&{1}&{2}\end{array}\right]$, as in exercise $39$. There, we found $A^{-1}=\left[\begin{array}{rrr} {-\displaystyle \frac{5}{7}}&{\displaystyle \frac{1}{7}}&{\displaystyle \frac{3}{7}}\\ {\displaystyle \frac{9}{7}}&{\displaystyle \frac{1}{7}}&{-\displaystyle \frac{4}{7}}\\ {\displaystyle \frac{3}{7}}&{-\displaystyle \frac{2}{7}}&{\displaystyle \frac{1}{7}}\end{array}\right]$ With $B=\left[\begin{array}{l} 2\\ 7/3\\ 10/3 \end{array}\right]$, the solution, $X=A^{-1}B$ equals $X=\left[\begin{array}{l} \frac{1}{7}(-10+\frac{7}{3}+10)\\ \frac{1}{7}(18+7/3-40/3)\\ \frac{6}{7}-\frac{2}{3}+\frac{10}{21} \end{array}\right]=\left[\begin{array}{l} 1/3\\ 1\\ \frac{18-14+10}{21} \end{array}\right]=\left[\begin{array}{l} 1/3\\ 1\\ \frac{14}{21} \end{array}\right]=\left[\begin{array}{l} 1/3\\ 1\\ 2/3 \end{array}\right]$ $x=1/3, \ y=1, \ z=2/3$ or $(1/3, \ 1, \ 2/3)$
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