Algebra 2 (1st Edition)

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

Chapter 3 Linear Systems and Matrices - 3.6 Multiplying Matrices - Guided Practice for Example 3 - Page 197: 4

Answer

$\begin{bmatrix}-13&1\\-21&9\\25&-13\end{bmatrix}$

Work Step by Step

We are given the matrices: $$A=\begin{bmatrix}-1&2\\-3&0\\4&1\end{bmatrix},\text{ }B=\begin{bmatrix}3&2\\-2&-1\end{bmatrix}, \text{ }C=\begin{bmatrix}-4&5\\1&0\end{bmatrix}.$$ Calculate $A(B-C)$: $$\begin{align*} A(B-C)&=\begin{bmatrix}-1&2\\-3&0\\4&1\end{bmatrix}\left(\begin{bmatrix}3&2\\-2&-1\end{bmatrix}-\begin{bmatrix}-4&5\\1&0\end{bmatrix}\right)\\ &=\begin{bmatrix}-1&2\\-3&0\\4&1\end{bmatrix}\cdot\begin{bmatrix}3-(-4)&2-5\\-2-1&-1-0\end{bmatrix}\\ &=\begin{bmatrix}-1&2\\-3&0\\4&1\end{bmatrix}\cdot\begin{bmatrix}7&-3\\-3&-1\end{bmatrix}\\ &=\begin{bmatrix}(-1)7+2(-3)&(-1)(-3)+2(-1)\\(-3)7+0(-3)&(-3)(-3)+0(-1)\\4(7)+1(-3)&4(-3)+1(-1)&\end{bmatrix}\\ &=\begin{bmatrix}-13&1\\-21&9\\25&-13\end{bmatrix}. \end{align*}$$
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