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: 41

Answer

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

Work Step by Step

The augmented matrix of the system is: $\begin{bmatrix} 2&1 &-8 |0\\ 3& -2 & -5 |0\\ 5&-6 &-3 | 0 \\ 3 &-5 &1 \end{bmatrix}$ with reduced row-echelon form: $\begin{bmatrix} 2&1 &-8 |0\\ 3& -2 & -5 |0\\ 5&-6 &-3 | 0 \\ 3 &-5 &1 \end{bmatrix} \approx^1 \begin{bmatrix} 3& -2 & -5 |0\\ 2&1 &-8 |0\\ 5&-6 &-3 | 0 \\ 3 &-5 &1 \end{bmatrix} \approx^2 \begin{bmatrix} 1& -3 & 3 |0\\ 2&1 &-8 |0\\ 5&-6 &-3 | 0 \\ 3 &-5 &1 \end{bmatrix} \approx^3 \begin{bmatrix} 1& -3 & 3 |0\\ 0&7&-14 |0\\ 0&9 &-18 | 0 \\ 0 &4 &-8 \end{bmatrix} \approx^4 \begin{bmatrix} 1& -3 & 3 |0\\ 0&1&-2 |0\\ 0&9 &-18 | 0 \\ 0 &4 &-8 \end{bmatrix} \approx^5 \begin{bmatrix} 1& 0 & -3 |0\\ 0&1&-2 |0\\ 0&0 &0 | 0 \\ 0 &0 &0|0 \end{bmatrix}$ $1.P_{12}$ $2.A_{21}(-1)$ $3.A_{12}(-2),A_{13}(-5),A_{14}(-3)$ $4.M_2(\frac{1}{7})$ $5.A_{21}(3),A_{23}(-9),A_{24}(-4)$ This matrix is now in row-echelon form. The solution set is: $x_1-3x_3=0$ $x_2-2x_3=0$ $x_3=t$ There is one free variable, which we take to be $x_3 = t$, where t can assume any complex value. Applying back substitution yields: $x_1-3t=0 \rightarrow x_1=t$ $x_2-2t=0 \rightarrow x_2=2t$ $x_3=t$ Hence, the solution is $(3t,2t,t)$
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