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 168: 44

Answer

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

Work Step by Step

The augmented matrix of the system is: $\begin{bmatrix} 2&-4 &6 |0\\ 3&-6 &9 |0\\ 1&-2 &3 | 0 \\ 5 &-10 &15|0 \end{bmatrix}$ with reduced row-echelon form: $\begin{bmatrix} 2&-4 &6 |0\\ 3&-6 &9 |0\\ 1&-2 &3 | 0 \\ 5 &-10 &15|0 \end{bmatrix}\approx^1 \begin{bmatrix} 1&-2 &3 |0\\ 3&-6 &9 |0\\ 2&-4 &6 | 0 \\ 5 &-10 &15|0 \end{bmatrix} \approx^2 \begin{bmatrix} 1&-2 &3 |0\\ 0&0 &0|0\\ 0&0 &0 | 0 \\ 0&0 &0|0 \end{bmatrix} $ $1.M_1(\frac{1}{2})$ $2.A_{12}(-3),A_{23}(-2),A_{24}(-5)$ This matrix is now in row-echelon form. The solution set is: $x_1-2x_2+3x_3=0$ $x_2=s$ $x_3=t$ There is one free variable, which we take to be $x_2=s,x_3 = t$, where t can assume any complex value. Applying back substitution yields: $x_1-2s+3t=0 \rightarrow x_1=2s-3t$ $x_2=s$ $x_3=t$ Hence, the solution is $(2s-3t,s,t)$
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