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: 18

Answer

The solution is $(1,-3,4,-4,2)$

Work Step by Step

The augmented matrix of the system is: $\begin{bmatrix} 2&-1 &2 &1 &-1 |11\\ 1 &-3 &-2 &-1 &-2| 2\\ 3& 1 & -2 & -1&1 |-2\\ 1 & 2& 1 & 2 & 3|-3\\ 5 & -3 & -3 & 1 &2 |2 \end{bmatrix}$ with reduced row-echelon form: $\begin{bmatrix} 2&-1 &2 &1 &-1 |11\\ 1 &-3 &-2 &-1 &-2| 2\\ 3& 1 & -2 & -1&1 |-2\\ 1 & 2& 1 & 2 & 3|-3\\ 5 & -3 & -3 & 1 &2 |2 \end{bmatrix} \approx^1\begin{bmatrix} 1 &-3 &-2 &-1 &-2| 2\\ 2&-1 &2 &1 &-1 |11\\ 3& 1 & -2 & -1&1 |-2\\ 1 & 2& 1 & 2 & 3|-3\\ 5 & -3 & -3 & 1 &2 |2 \end{bmatrix}\approx^2\begin{bmatrix} 1 &-3 &-2 &-1 &-2| 2\\ 2&5 &7 &3 &3 |7\\ 0& 10 & 4 & 2&7 |-8\\ 0 & 5&3 & 3 & 5|-5\\ 0 & 12 &7 &6 &12 |-8 \end{bmatrix}\approx^3\begin{bmatrix} 1 &-3 &-2 &-1 &-2| 2\\ 0&1 &\frac{7}{5} &\frac{3}{5} &\frac{3}{5} |\frac{7}{5}\\ 0& 10 & 4 & 2&7 |-8\\ 0 & 5&3 & 3 & 5|-5\\ 0 & 12 &7 &6 &12 |-8 \end{bmatrix} \approx^4\begin{bmatrix} 1 &0 &\frac{11}{5} &\frac{4}{5} &\frac{-1}{5}| \frac{31}{5}\\ 0&1 &\frac{7}{5} &\frac{3}{5} &\frac{3}{5} |\frac{7}{5}\\ 0& 0&-10 & -4 & 1 |-22\\ 0 & 0&-4 & 0 & 2|-12\\ 0 & 0 &\frac{-49}{5} &\frac{-6}{5} &\frac{24}{5} |\frac{-124}{5} \end{bmatrix} \approx^5\begin{bmatrix} 1 &0 &\frac{11}{5} &\frac{4}{5} &\frac{-1}{5}| \frac{31}{5}\\ 0&1 &\frac{7}{5} &\frac{3}{5} &\frac{3}{5} |\frac{7}{5}\\ 0& 0&-10 & -4 & 1 |-22\\ 0 & 0&0 & 1 & 1|-2\\ 0 & 0 &\frac{-49}{5} &\frac{-6}{5} &\frac{24}{5} |\frac{-124}{5} \end{bmatrix} \approx^6 \begin{bmatrix} 1 &0 &0 &\frac{-2}{25} &\frac{-1}{50}| \frac{34}{25}\\ 0&1 &0 &\frac{1}{25} &\frac{37}{50} |\frac{-42}{25}\\ 0& 0&1&\frac{2}{5} & -\frac{1}{10} |\frac{11}{5}\\ 0 & 0&0 & \frac{8}{5} & \frac{8}{5} |-\frac{16}{5} \\ 0 & 0 &0&\frac{68}{25} &\frac{191}{50} |\frac{-81}{25} \end{bmatrix} \approx^7 \begin{bmatrix} 1 &0 &0 &\frac{-2}{25} &\frac{-1}{50}| \frac{34}{25}\\ 0&1 &0 &\frac{1}{25} &\frac{37}{50} |\frac{-42}{25}\\ 0& 0&1&\frac{2}{5} & -\frac{1}{10} |\frac{11}{5}\\ 0 & 0&0 &1 &1 |-2 \\ 0 & 0 &0&\frac{68}{25} &\frac{191}{50} |\frac{-81}{25} \end{bmatrix} \approx^8 \begin{bmatrix} 1 &0 &0 &0 &\frac{1}{10}| \frac{6}{5}\\ 0&1 &0 &0 &\frac{7}{10} |\frac{-8}{5}\\ 0& 0&1&0& -\frac{1}{2} |3\\ 0 & 0&0 &1 &1 |-2 \\ 0 & 0 &0&0&\frac{11}{10} |\frac{11}{5} \end{bmatrix} \approx^9 \begin{bmatrix} 1 &0 &0 &0 &\frac{1}{10}| \frac{6}{5}\\ 0&1 &0 &0 &\frac{7}{10} |\frac{-8}{5}\\ 0& 0&1&0& -\frac{1}{2} |3\\ 0 & 0&0 &1 &1 |-2 \\ 0 & 0 &0&0&1 |2 \end{bmatrix} \approx^10 \begin{bmatrix} 1 &0 &0 &0 &0| 1\\ 0&1 &0 &0 &0 |-3\\ 0& 0&1&0&0|4\\ 0 & 0&0 &1 &0 |-4 \\ 0 & 0 &0&0&1 |2 \end{bmatrix}$ $1.P_{12}$ $2.A_{12}(-2), A_{13}(-3),A_{14}(-1),A_{15}(-5)$ $3.M_2(-\frac{11}{5})$ $4.A_{21}(3),A_{23}(-10),A_{25}(-12)$ $5.M_2(-\frac{1}{10})$ $6.A_{31}(-\frac{11}{5}),A_{32}(-\frac{7}{5}),A_{34}(4),A_{35}(\frac{49}{5})$ $7.M_4(\frac{5}{8})$ $8.A_{41}(\frac{2}{25}),A_{42}(-\frac{1}{25}),A_{43}(-\frac{2}{5}),A_{45}(\frac{-68}{25}),M_5(\frac{10}{11})$ $9.A_{51}(-\frac{1}{10}),A_{52}(-\frac{7}{10}),A_{53}(\frac{1}{2}),A_{54}(-1)$ This matrix is now in row-echelon form. The equivalent system is: $x_1=1$ $x_2=-3$ $x_3=4$ $x_4=-4$ $x_5=2$ The solution is $(1,-3,4,-4,2)$
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