Algebra 2 Common Core

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

Chapter 12 - Matrices - 12-2 Matrix Multiplication - Lesson Check - Page 777: 2

Answer

$3B-2A=\begin{bmatrix} -3 & 11 \\ -10 & 6 \end{bmatrix}$

Work Step by Step

Multiplying each element of $ B= \begin{bmatrix} 1 & 3 \\ -2 & 2 \end{bmatrix} $ by $3,$ then \begin{align*} 3B&= \begin{bmatrix} 1(3) & 3(3) \\ -2(3) & 2(3) \end{bmatrix} \\\\&= \begin{bmatrix} 3 & 9 \\ -6 & 6 \end{bmatrix} .\end{align*} Multiplying each element of $ A= \begin{bmatrix} 3 & -1 \\ 2 & 0 \end{bmatrix} $ by $2,$ then \begin{align*} 2A&= \begin{bmatrix} 3(2) & -1(2) \\ 2(2) & 0(2) \end{bmatrix} \\\\&= \begin{bmatrix} 6 & -2 \\ 4 & 0 \end{bmatrix} .\end{align*} Combining the results above gives \begin{align*} 3B-2A&= \begin{bmatrix} 3 & 9 \\ -6 & 6 \end{bmatrix} - \begin{bmatrix} 6 & -2 \\ 4 & 0 \end{bmatrix} \\\\&= \begin{bmatrix} 3-6 & 9-(-2) \\ -6-4 & 6-0 \end{bmatrix} \\\\&= \begin{bmatrix} 3-6 & 9+2 \\ -6-4 & 6-0 \end{bmatrix} \\\\&= \begin{bmatrix} -3 & 11 \\ -10 & 6 \end{bmatrix} .\end{align*} Hence, $ 3B-2A=\begin{bmatrix} -3 & 11 \\ -10 & 6 \end{bmatrix} .$
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