Elementary Linear Algebra 7th Edition

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

Chapter 1 - Systems of Linear Equations - Review Exercises - Page 36: 45

Answer

$x_1=-4t$, $x_2=-\frac{1}{2}t$, $x_3=t$

Work Step by Step

The augmented matrix is given by: $\left[ {\begin{array}{*{20}{c}} 2&{ - 8}&4&0\\ 3&{ - 10}&7&0\\ 0&{10}&5&0 \end{array}} \right]$ Row reducing this matrix gives $\begin{array}{l} \left[ {\begin{array}{*{20}{c}} 2&{ - 8}&4&0\\ 3&{ - 10}&7&0\\ 0&{10}&5&0 \end{array}} \right]\\ {R_1} \to \frac{{{R_1}}}{2}\\ \left[ {\begin{array}{*{20}{c}} 1&{ - 4}&2&0\\ 3&{ - 10}&7&0\\ 0&{10}&5&0 \end{array}} \right]\\ {R_2} \to {R_2} - 3{R_1}\\ \left[ {\begin{array}{*{20}{c}} 1&{ - 4}&2&0\\ 0&2&1&0\\ 0&{10}&5&0 \end{array}} \right]\\ {R_3} \to {R_3} - 5{R_2}\\ \left[ {\begin{array}{*{20}{c}} 1&{ - 4}&2&0\\ 0&2&1&0\\ 0&0&0&0 \end{array}} \right]\\ {R_1} \to {R_1} + 2{R_2}\\ \left[ {\begin{array}{*{20}{c}} 1&0&4&0\\ 0&2&1&0\\ 0&0&0&0 \end{array}} \right]\\ {R_2} \to \frac{{{R_2}}}{2}\\ \left[ {\begin{array}{*{20}{c}} 1&0&4&0\\ 0&1&{1/2}&0\\ 0&0&0&0 \end{array}} \right] \end{array}$ This means that $x_3$ is a free variable. Let $x_3=t$; then $x_1=-4x_3=-4t$, $x_2=-\frac{1}{2}x_3=-\frac{1}{2}t$
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