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 165: 5

Answer

The solution is $(1-t,2-3t,t)$

Work Step by Step

The augmented matrix of the system is: $\begin{bmatrix} 3& -1 &0 |1\\ 2& 1 &5| 4\\ 7 & -5 & -8|-3 \end{bmatrix}$ with reduced row-echelon form: $\begin{bmatrix} 3& -1 &0 |1\\ 2& 1 &5| 4\\ 7 & -5 & -8|-3 \end{bmatrix} \approx^1 \begin{bmatrix} 1& -2 &-5 |-3\\ 2& 1 &5| 4\\ 7 & -5 & -8|-3 \end{bmatrix} \approx^2\begin{bmatrix} 1& -2 &-5 |-3\\ 0& 5 &15| 10\\ 0 & 9 & 27|18 \end{bmatrix} \approx^3 \begin{bmatrix} 1& -2 &-5 |-3\\ 0& 1 &3| 2\\ 0 & 9 & 27|18 \end{bmatrix} \approx^4 \begin{bmatrix} 1& 0 &1 |1\\ 0& 1 &3| 2\\ 0 & 0 & 0|0 \end{bmatrix} $ The equivalent system is: $x_1+x_3=1$ $x_2+3x_3=2$ $x_3=t$ There is one free variable, which we take to be $x_3 = t$, where t can assume any complex value. Applying back substitution yields: $x_1=1-t$ $x_2=2-3t$ $x_3=t$ The solution is $(1-t,2-3t,t)$
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