Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 3 Linear Systems and Matrices - 3.7 Evaluate Determinants and Apply Cramer's Rule - Guided Practice for Examples 3 and 4 - Page 207: 6

Answer

$x=4,y=-2$

Work Step by Step

We know that for a matrix \[ \left[\begin{array}{rr} a & b \\ c &d \\ \end{array} \right] \] the determinant is $D=ad-bc.$ Thus the determinant of the coefficient matrix is: $D=4\cdot(-2)-7\cdot(-3)=8+21=13.$ Then applying Cramer's Rule: $x=\frac{\begin{vmatrix} 2 & 7 \\ -8 & -2 \\ \end{vmatrix}}{13}=\frac{2\cdot(-2)-8\cdot(-8)}{13}=\frac{52}{13}=4$ $y=\frac{\begin{vmatrix} 4 & 2 \\ -3 & -8 \\ \end{vmatrix}}{13}=\frac{4\cdot(-8)-2\cdot(-3)}{13}=\frac{-26}{13}=-2$ Thus $x=4,y=-2$
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