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: 7

Answer

The solution is $(2+\frac{1}{2}s-\frac{1}{2}t,s,t)$

Work Step by Step

The augmented matrix of the system is: $\begin{bmatrix} 6& -3 &3 |12\\ 2& -1 &1| 4\\ -4 & 2 & -2|8 \end{bmatrix}$ with reduced row-echelon form: $\begin{bmatrix} 6& -3 &3 |12\\ 2& -1 &1| 4\\ -4 & 2 & -2|8 \end{bmatrix} \approx^1\begin{bmatrix} 1& -\frac{1}{2} & -\frac{1}{2} |2\\ 2& -1 &1| 4\\ -4 & 2 & -2|-8 \end{bmatrix} \approx^2\begin{bmatrix} 1& -\frac{1}{2} & -\frac{1}{2} |2\\ 0& 0 &0| 0\\ 0 & 0 & 0|0 \end{bmatrix}$ The equivalent system is: $x_1-\frac{1}{2} x_2+\frac{1}{2} x_3=2$ $x_2=s$ $x_3 = t$ There are two free variables, which we take to be $x_2=s,x_3 = t$, where t and s can assume any complex value. Applying back substitution yields: $x_1-\frac{1}{2}s+\frac{1}{2}t=2 \rightarrow x_1=2+\frac{1}{2}s-\frac{1}{2}t$ $x_2=s$ $x_3 = t$ The solution is $(2+\frac{1}{2}s-\frac{1}{2}t,s,t)$
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