Algebra 2 Common Core

Published by Prentice Hall
ISBN 10: 0133186024
ISBN 13: 978-0-13318-602-4

Chapter 12 - Matrices - 12-3 Determinants and Inverses - Practice and Problem-Solving Exercises - Page 790: 68

Answer

$X = \begin{bmatrix} -10 & 19 \\ -20 & 7 \end{bmatrix}$

Work Step by Step

Using the properties of matrices, the given matrix equation, $ 2X+3\begin{bmatrix} 4 & -6 \\ 8 & -3 \end{bmatrix} = \begin{bmatrix} -8 & 20 \\ -16 & 5 \end{bmatrix} ,$ is equivalent to \begin{align*}\require{cancel} 2X+\begin{bmatrix} 4(3) & -6(3) \\ 8(3) & -3(3) \end{bmatrix} &= \begin{bmatrix} -8 & 20 \\ -16 & 5 \end{bmatrix} \\\\ 2X+\begin{bmatrix} 12 & -18 \\ 24 & -9 \end{bmatrix} &= \begin{bmatrix} -8 & 20 \\ -16 & 5 \end{bmatrix} \\\\ 2X &= \begin{bmatrix} -8 & 20 \\ -16 & 5 \end{bmatrix} - \begin{bmatrix} 12 & -18 \\ 24 & -9 \end{bmatrix} \\\\ 2X &= \begin{bmatrix} -8-12 & 20-(-18) \\ -16-24 & 5-(-9) \end{bmatrix} \\\\ 2X &= \begin{bmatrix} -8-12 & 20+18 \\ -16-24 & 5+9 \end{bmatrix} \\\\ 2X &= \begin{bmatrix} -20 & 38 \\ -40 & 14 \end{bmatrix} \\\\ \left(\dfrac{1}{2}\right)(2X) &= \dfrac{1}{2}\begin{bmatrix} -20 & 38 \\ -40 & 14 \end{bmatrix} \\\\ X &= \begin{bmatrix} -20\left(\dfrac{1}{2}\right) & 38\left(\dfrac{1}{2}\right) \\ -40\left(\dfrac{1}{2}\right) & 14\left(\dfrac{1}{2}\right) \end{bmatrix} \\\\ X &= \begin{bmatrix} -10 & 19 \\ -20 & 7 \end{bmatrix} .\end{align*} Hence, the solution is $ X = \begin{bmatrix} -10 & 19 \\ -20 & 7 \end{bmatrix} .$
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