Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 2 - Matrices and Systems of Linear Equations - 2.5 Gaussian Elimination - Problems - Page 166: 11

Answer

The system is inconsistent

Work Step by Step

The augmented matrix of the system is: $\begin{bmatrix} 1 &2& -1 &1 |1\\ 2&-3 &1 &-1| 2\\ 1 & -5 & 2 & -2|1\\ 4 & 1 & -1 & 1 |3 \end{bmatrix}$ with reduced row-echelon form: $\begin{bmatrix} 1 &2& -1 &1 |1\\ 2&-3 &1 &-1| 2\\ 1 & -5 & 2 & -2|1\\ 4 & 1 & -1 & 1 |3 \end{bmatrix}\approx^1\begin{bmatrix} 1 &2& -1 &1 |1\\ 0&-7 &3 &-3|0\\ 0 &-7 &3 &-3|0\\ 0 &-7 &3 &-3 |-1 \end{bmatrix} \approx^2 \begin{bmatrix} 1 &2& -1 &1 |1\\ 0&1 &-\frac{3}{7} &\frac{3}{7}|0\\ 0 &-7 &3 &-3|0\\ 0 &-7 &3 &-3 |-1 \end{bmatrix} \approx^3 \begin{bmatrix} 1 &2& -1 &1 |1\\ 0&1 &-\frac{3}{7} &\frac{3}{7}|0\\ 0 &0 &0 &0|0\\ 0 &0 &0 &0 |-1 \end{bmatrix} \approx^4 \begin{bmatrix} 1 &2& -1 &1 |1\\ 0&1 &-\frac{3}{7} &\frac{3}{7}|0\\ 0 &0 &0 &0|-1\\ 0 &0 &0 &0 |0 \end{bmatrix} \approx^5 \begin{bmatrix} 1 &2& -1 &1 |1\\ 0&1 &-\frac{3}{7} &\frac{3}{7}|0\\ 0 &0 &0 &0|1\\ 0 &0 &0 &0 |0 \end{bmatrix}$ The system is inconsistent since $rank(A) \lt rank (A^\ne)$
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