College Algebra (11th Edition)

Published by Pearson
ISBN 10: 0321671791
ISBN 13: 978-0-32167-179-0

Chapter 5 - Section 5.8 - Matrix Inverses - 5.8 Exercises - Page 567: 36

Answer

$\begin{bmatrix} x \\ y \end{bmatrix}= \begin{bmatrix} 2 \\ 3 \end{bmatrix} $

Work Step by Step

We will write the system of equations as follows: $\begin{bmatrix} 1 & 1 \\ 1 & -1 \end{bmatrix} \begin{bmatrix} x \\ y \end{bmatrix}=\begin{bmatrix} 5 \\ -1 \end{bmatrix} $ Next, we will find the inverse of the left matrix factor as follows: $\dfrac{1}{(1)(-1)-(1)(1)}\begin{bmatrix} -1 & -1 \\ -1 & 1 \end{bmatrix} $ This yields to: $\begin{bmatrix} 1/2 & 1/2 \\ 1/2 & -1/2 \end{bmatrix} $ Therefore, the value of $x,y$ can be calculated as: $\begin{bmatrix} x \\ y \end{bmatrix}=\begin{bmatrix} 1/2 & 1/2 \\ 1/2 & -1/2 \end{bmatrix} \begin{bmatrix} 5 \\ -1 \end{bmatrix} $ or, $\begin{bmatrix} x \\ y \end{bmatrix}=\begin{bmatrix} (1/2)(5)+(1/2)(-1) \\ (1/2)(5) - (1/2)(-1) \end{bmatrix} = \begin{bmatrix} 2 \\ 3 \end{bmatrix} $ Hence, our result is: $\begin{bmatrix} x \\ y \end{bmatrix}= \begin{bmatrix} 2 \\ 3 \end{bmatrix} $
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