Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 11 - Systems of Equations and Inequalities - 11.3 Systems of Linear Equations: Determinants - 11.3 Assess Your Understanding - Page 742: 33

Answer

$(x,y,z) =(1,3,-2)$

Work Step by Step

The given system of equations is $\left\{\begin{matrix} x& +y &-z&=&6\\ 3x& -2y & +z&=&-5\\ x& +3y &-2z &=&14 \end{matrix}\right.$ The formula to determine the determinant is $D=\begin{vmatrix} a& b &c \\ d& e &f \\ g &h &i \end{vmatrix}=a\begin{vmatrix} e& f \\ h&i \end{vmatrix}-b\begin{vmatrix} d& f \\ g&i \end{vmatrix}+c\begin{vmatrix} d& e \\ g&h \end{vmatrix}$ Determinant $D$ consists of the $x,y$ and $z$ coefficients. $D=\begin{vmatrix} 1& 1 &-1 \\ 3& -2 &1 \\ 1 &3 &-2 \end{vmatrix}=-3$ For determinant $D_x$ replace the $x−$ coefficients with the constants. $D_x=\begin{vmatrix} 6& 1 &-1 \\ -5& -2 &1 \\ 14 &3 &-2 \end{vmatrix}=-3$ For determinant $D_y$ replace the $y−$ coefficients with the constants. $D_y=\begin{vmatrix} 1& 6 &-1 \\ 3& -5 &1 \\ 1 &14 &-2 \end{vmatrix}=-9$ For determinant $D_z$ replace the $z−$ coefficients with the constants. $D_z=\begin{vmatrix} 1& 1 &6 \\ 3& -2 &-5 \\ 1 &3 &14 \end{vmatrix}=6$ By using Cramer's rule we have. $x=\dfrac{D_x}{D}=\dfrac{-3}{-3}=1$ and $y=\dfrac{D_y}{D}=\dfrac{-9}{-3}=3$ and $z=\dfrac{D_z}{D}=\dfrac{6}{-3}=-2$ Hence, the solution set is $(x,y,z) =(1,3,-2)$.
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