Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 11 - Systems of Equations and Inequalities - 11.2 Systems of Linear Equations: Matrices - 11.2 Assess Your Understanding - Page 731: 61

Answer

Consistent Solution set: $\left\{\left(-3,\dfrac{1}{2},1\right)\right\}$

Work Step by Step

We are given the system of equations: $\begin{cases} x+2y-z=-3\\ 2x-4y+z=-7\\ -2x+2y-3z=4 \end{cases}$ Write the augmented matrix: $\begin{bmatrix} 1&2&-1&|&-3\\2&-4&1&|&-7\\-2&2&-3&|&4\end{bmatrix}$ Perform row operations to bring the matrix to the reduced row echelon form: $R_2=-2r_1+r_2$ $\begin{bmatrix} 1&2&-1&|&-3\\0&-8&3&|&-1\\-2&2&-3&|&4\end{bmatrix}$ $R_3=2r_1+r_3$ $\begin{bmatrix}1&2&-1&|&-3\\0&-8&3&|&-1\\0&6&-5&|&-2\end{bmatrix}$ $R_2=-\dfrac{1}{8}$ $\begin{bmatrix}1&2&-1&|&-3\\0&1&-\frac{3}{8}&|&\frac{1}{8}\\0&6&-5&|&-2\end{bmatrix}$ $R_3=-6r_2+r_3$ $\begin{bmatrix}1&2&-1&|&-3\\0&1&-\frac{3}{8}&|&\frac{1}{8}\\0&0&-\frac{11}{4}&|&-\frac{11}{4}\end{bmatrix}$ $R_3=-\dfrac{4}{11}r_3$ $\begin{bmatrix}1&2&-1&|&-3\\0&1&-\frac{3}{8}&|&\frac{1}{8}\\0&0&1&|&1\end{bmatrix}$ Write the corresponding system of equations: $\begin{cases} x+2y-z=-3\\ y-\frac{3}{8}z=\frac{1}{8}\\ z=1 \end{cases}$ Solve the system by back substitution: $z=1$ $y-\frac{3}{8}z=\frac{1}{8}$ $y-\frac{3}{8}=\frac{1}{8}$ $y=\frac{1}{2}$ $x+2y-z=-3$ $x+2\left(\dfrac{1}{2}\right)-1=-3$ $x+1-1=-3$ $x=-3$ The system is consistent. The solution is: $\left\{\left(-3,\dfrac{1}{2},1\right)\right\}$
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