Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 8 - Section 8.2 - Inconsistent and Dependent Systems and Their Applications - Exercise Set - Page 903: 26

Answer

a) The system represented is; $\begin{align} & 2w+17x-23y+40z=0 \\ & 2w+5x+y+3z=0 \\ & x-2y+3z=0 \end{align}$ b) The solution for this system is $\left[ \begin{matrix} -5.5 \\ 2 \\ 1 \\ 0 \\ \end{matrix} \right]$

Work Step by Step

(a) System represented by $ A $ can be written by multiplying $\left[ A \right]\times \left[ X \right]=\left[ 0 \right]$ Where A is augmented matrix and X is variable matrix. So, $\left[ \begin{matrix} 2 & 17 & -23 & 40 & 0 \\ 2 & 5 & 1 & 3 & 0 \\ 0 & 1 & -2 & 3 & 0 \\ \end{matrix} \right]\times \left[ \begin{matrix} W \\ X \\ Y \\ Z \\ 1 \\ \end{matrix} \right]=\left[ \begin{align} & 0 \\ & 0 \\ & 0 \\ & 0 \\ & 0 \\ \end{align} \right]$ So, $\begin{align} & 2w+17x-23y+40z=0 \\ & 2w+5x+y+3z=0 \\ & x-2y+3z=0 \end{align}$ Hence, the system represented is; $\begin{align} & 2w+17x-23y+40z=0 \\ & 2w+5x+y+3z=0 \\ & x-2y+3z=0 \end{align}$ (b) Now since $ rref\left( A \right)=\left[ \begin{matrix} 1 & 0 & 5.5 & 0 & 0 \\ 0 & 1 & -2 & 0 & 0 \\ 0 & 0 & 0 & 1 & 0 \\ \end{matrix} \right]$ So, from here we get, $\begin{align} & w+5.5y=0 \\ & x-2y=0 \\ & z=0 \end{align}$ So, $\begin{align} & w=-5.5y \\ & x=2y \\ & z=0 \end{align}$ So, the solution will be $\left[ \begin{matrix} -5.5 \\ 2 \\ 1 \\ 0 \\ \end{matrix} \right]$ Hence, the solution to given problem will be $\left[ \begin{matrix} -5.5 \\ 2 \\ 1 \\ 0 \\ \end{matrix} \right]$.
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