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: 12

Answer

The solution is $(1-2r+3s-t,r,2-4s+3t,s,t)$

Work Step by Step

The augmented matrix of the system is: $\begin{bmatrix} 1 &2& 1 &1 & -2 |3\\ 0&0 1 &&4 &-3| 2\\ 2& 4 & -1 &-10 & 5|0 \end{bmatrix}$ with reduced row-echelon form: $\begin{bmatrix} 1 &2& 1 &1 & -2 |3\\ 0&0 1 &&4 &-3| 2\\ 2& 4 & -1 &-10 & 5|0 \end{bmatrix} \approx^1\begin{bmatrix} 1 &2& 1 &1 & -2 |3\\ 0&0 &1 &4 &-3| 2\\ 0& 0 & -3 &-12 & 9|-6 \end{bmatrix} \approx^2 \begin{bmatrix} 1 &2& 1 &1 & -2 |3\\ 0&0 &1 &4 &-3| 2\\ 0& 0 & 0 &0 & 0|0 \end{bmatrix}$ $x_1+2x_2+x_3+x_4-2x_5=3$ $x_3+4x_4-3x_5=2$ $x_4=s$ $ x_5 = t$ There are three free variables, which we take to be $x_2=r,x_4=s, x_5 = t$, where s and t can assume any complex values. Applying back substitution yields: $x_2=r$ $x_4=s$ $ x_5 = t$ $x_3+4s-3t=2 \rightarrow x_3=2-4s+3t$ $x_1+2r+2-4s+3t+s-2t=3 \rightarrow x_1=1-2r+3s-t$ The solution is $(1-2r+3s-t,r,2-4s+3t,s,t)$
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