College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter 8 - Section 8.1 - Systems of Linear Equations: Substitution and Elimination - 8.1 Assess Your Understanding - Page 556: 50

Answer

$\{(x,y,z)\ |\ x=\displaystyle \frac{2+4y}{7},\ z=\displaystyle \frac{4-13y}{7},\ y\in \mathbb{R}\}$

Work Step by Step

$\left\{\begin{array}{lllll} 2x & -3y & -z & =0 & \\ 3x & +2y & +2z & =2 & /R_{2}=r_{2}+2r_{1}\\ x & +5y & +3z & =0 & /R_{3}=r_{3}+3r_{1} \end{array}\right.$ ... Eliminate $z$ in eq. 2 and 3 $\left\{\begin{array}{lllll} 2x & -3y & -z & =0 & \\ 7x & -4y & & =2 & \\ 7x & -4y & & =0 & /R_{3}=r_{3}-r_{2} \end{array}\right.$ ... Eliminate y in equation 3 $\left\{\begin{array}{lllll} 2x & -3y & -z & =0 & (1)\\ 7x & -4y & & =2 & (2)\\ & & 0 & =0 & (3) \end{array}\right.$ Equation 3 is 0=0, which is always satisfied. The system is consistent and dependent. Let $y$ be the parameter, $y\in \mathbb{R}.$ $(2)\displaystyle \Rightarrow 7x=2+4y\Rightarrow x=\frac{2+4y}{7}$ $(1)\displaystyle \Rightarrow z=2x-3y=\frac{2(2+4y)}{7}-\frac{21y}{7}=\frac{4-13y}{7}$ Solution set: $\{(x,y,z)\ |\ x=\displaystyle \frac{2+4y}{7},\ z=\displaystyle \frac{4-13y}{7},\ y\in \mathbb{R}\}$
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