College Algebra (10th Edition)

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

Chapter 8 - Section 8.3 - Systems of Linear Equations: Determinants - 8.3 Assess Your Understanding - Page 582: 29

Answer

$(\displaystyle \frac{3}{2},1)$

Work Step by Step

Cramer's rule $\left\{\begin{array}{l}{a x+b y=s}\\{cx+dy=t}\end{array}\right.$ $D=\left|\begin{array}{ll}{a}&{b}\\{c}&{d}\end{array}\right|,D_{x}=\left|\begin{array}{ll}{s}&{b}\\{t}&{d}\end{array}\right|,D_{y}=\left|\begin{array}{ll}{a}&{s}\\{c}&{t}\end{array}\right|,$ If $D\displaystyle \neq 0,\qquad x=\frac{D_{x}}{D}\quad y=\frac{D_{y}}{D}$ --- $\displaystyle \left\{\begin{array}{r}{2 x+3 y=6}\\{x-y=\frac{1}{2}}\end{array}\right.\Rightarrow\left[\begin{array}{ll} a & b\\ c & d \end{array}\right]=\displaystyle \left[\begin{array}{ll} 2 & 3\\ 1 & -1 \end{array}\right],\quad \left[\begin{array}{l} s\\ t \end{array}\right]=\left[\begin{array}{l} 6\\ 1/2 \end{array}\right]$ $\begin{array}{lllll} D=\left|\begin{array}{ll} 2 & 3\\ 1 & -1 \end{array}\right|= & & D_{x}=\left|\begin{array}{ll} 6 & 3\\ 1/2 & -1 \end{array}\right|= & & D_{y}=\left|\begin{array}{ll} 2 & 6\\ 1 & 1/2 \end{array}\right|=\\ =-2-3 & & =-6-3/2 & & =1-6\\ =-5\neq 0 & & =-15/2 & & =-5\\ & & & & \end{array}$ $x=\displaystyle \frac{D_{x}}{D}=\frac{8}{40}=\frac{-15/2}{-5}=\frac{3}{2}$ $y=\displaystyle \frac{D_{y}}{D}=\frac{12}{40}=\frac{-5}{-5}=1$ Solution: $(x,y)=(\displaystyle \frac{3}{2},1)$
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