Intermediate Algebra for College Students (7th Edition)

Published by Pearson
ISBN 10: 0-13417-894-7
ISBN 13: 978-0-13417-894-3

Chapter 3 - Section 3.4 - Matrix Solutions to Linear Systems - Exercise Set - Page 229: 30

Answer

$\{(2,0,-1)\}$.

Work Step by Step

The given system of equations is $3x+2y+3z=3$ $4x-5y+7z=1$ $2x+3y-2z=6$ The augmented matrix is $\Rightarrow \left[\begin{array}{ccc|c} 3 & 2 & 3& 3\\ 4 &-5 & 7& 1 \\ 2&3&-2&6 \end{array}\right]$ Perform $R_1\Rightarrow R_1/(3)$ $\Rightarrow \left[\begin{array}{ccc|c} 3/(3) & 2/(3) & 3/(3)& 3/(3)\\ 4 &-5 & 7& 1 \\ 2&3&-2&6 \end{array}\right]$ Simplify. $\Rightarrow \left[\begin{array}{ccc|c} 1 & 2/3 & 1& 1\\ 4 &-5 & 7& 1 \\ 2&3&-2&6 \end{array}\right]$ Perform $R_2\rightarrow R_2-4 R_1$ and $R_3\rightarrow R_3-2 R_1$. $\Rightarrow \left[\begin{array}{ccc|c} 1 & 2/3 & 1& 1\\ 4-4(1) &-5-4(2/3) & 7-4(1)& 1-4(1) \\ 2-2(1)&3-2(2/3)&-2-2(1)&6-2(1) \end{array}\right]$ Simplify. $\Rightarrow \left[\begin{array}{ccc|c} 1 & 2/3 & 1& 1\\ 0 &-23/3 &3& -3 \\ 0&5/3&-4&4 \end{array}\right]$ Perform $R_2\Rightarrow R_2(-3/23)$ $\Rightarrow \left[\begin{array}{ccc|c} 1 & 2/3 & 1& 1\\ 0(-3/23) &-23/3(-3/23) &3(-3/23)& -3(-3/23) \\ 0&5/3&-4&4 \end{array}\right]$ Simplify. $\Rightarrow \left[\begin{array}{ccc|c} 1 & 2/3 & 1& 1\\ 0 &1 &-9/23& 9/23 \\ 0&5/3&-4&4 \end{array}\right]$ Perform $R_1\rightarrow R_1-(2/3) R_2$ and $R_3\rightarrow R_3-(5/3) R_2$. $\Rightarrow \left[\begin{array}{ccc|c} 1-(2/3)(0) & 2/3-(2/3)(1) & 1-(2/3)(-9/23)& 1-(2/3)(9/23)\\ 0 &1 &-9/23& 9/23 \\ 0-(5/3)(0)&5/3-(5/3)(1)&-4-(5/3)(-9/23)&4-(5/3)(9/23) \end{array}\right]$ Simplify. $\Rightarrow \left[\begin{array}{ccc|c} 1 &0 & 29/23& 17/23\\ 0 &1 &-9/23& 9/23 \\ 0&0&-77/23&77/23 \end{array}\right]$ Perform $R_3\rightarrow R_3(-23/77)$. $\Rightarrow \left[\begin{array}{ccc|c} 1 &0 & 29/23& 17/23\\ 0 &1 &-9/23& 9/23 \\ 0(-23/77)&0(-23/77)&-77/23(-23/77)&77/23(-23/77) \end{array}\right]$ Simplify. $\Rightarrow \left[\begin{array}{ccc|c} 1 &0 & 29/23& 17/23\\ 0 &1 &-9/23& 9/23 \\ 0&0&1&-1 \end{array}\right]$ Perform $R_1\rightarrow R_1-(29/23)R_3$ and $R_2\rightarrow R_2+(9/23) R_3$. $\Rightarrow \left[\begin{array}{ccc|c} 1-(29/23)(0) &0-(29/23)(0) & 29/23-(29/23)(1)& 17/23-(29/23)(-1)\\ 0+(9/23)(0) &1+(9/23)(0) &-9/23+(9/23)(1)& 9/23+(9/23)(-1) \\ 0&0&1&-1 \end{array}\right]$ Simplify. $\Rightarrow \left[\begin{array}{ccc|c} 1 &0 & 0& 2\\ 0 &1 &0& 0 \\ 0&0&1&-1 \end{array}\right]$ Use back substitution to solve the linear system. $\Rightarrow x=2$. and $\Rightarrow y=0$. and $\Rightarrow z=-1$. The solution set is $\{(x,y,z)\}=\{(2,0,-1)\}$.
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