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 599: 81

Answer

Solution set = $\displaystyle \{(x,y,z)\ | \ x=\frac{1}{5}-\frac{1}{5}z,\ y=-\frac{6}{5}+\frac{1}{5}z, z\in \mathbb{R}\}$

Work Step by Step

Method: Gauss-Jordan. Row reduce the augmented matrix: $\left[\begin{array}{rrr|r} 2 & -3 & 1 & 4 \\ -3 & 2 & -1 & -3 \\ 0 & -5 & 1 & 6 \end{array}\right]\qquad\left\{\begin{array}{l} R_{1}=2r_{1}+r_{2}.\\ R_{2}=3r_{1}+2r_{2}.\\ . \end{array}\right\}\rightarrow$ $\rightarrow\left[\begin{array}{rrr|r} 1 & -4 & 1 & 5 \\ 0 & -5 & 1 & 6 \\ 0 & -5 & 1 & 6 \end{array}\right]\qquad\left\{\begin{array}{l} R_{1}=r_{1}-\frac{4}{5}r_{2}.\\ R_{2}=r_{2}\div(-5).\\ R_{3}=r_{3}-r_{2}. \end{array}\right\}\rightarrow$ $\rightarrow\left[\begin{array}{rrr|r} 1 & 0 & 1/5 & 1/5 \\ 0 & 1 & -1/5 & -6/5 \\ 0 & 0 & 0 & 0 \end{array}\right]\qquad$ The system is consistent (the last row represents 0=0, which is always satisfied). Taking $z\in \mathbb{R}$ as a parameter, we have: Eq.2 $\Rightarrow y=-\displaystyle \frac{6}{5}+\frac{1}{5}z,$ Eq.$1 \displaystyle \Rightarrow x=\frac{1}{5}-\frac{1}{5}z$ Solution set = $\displaystyle \{(x,y,z)\ | \ x=\frac{1}{5}-\frac{1}{5}z,\ y=-\frac{6}{5}+\frac{1}{5}z, z\in \mathbb{R}\}$
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