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: 41

Answer

$\begin{bmatrix} x \\ y \end{bmatrix}= \begin{bmatrix} -\frac{1}{2} \\ \frac{2}{3} \end{bmatrix} $

Work Step by Step

We will write the system of equations as follows: $\begin{bmatrix} 6 & 9 \\ -8 & 3 \end{bmatrix} \begin{bmatrix} x \\ y \end{bmatrix}=\begin{bmatrix} 3 \\ 6 \end{bmatrix} $ Next, we will find the inverse of the left matrix factor as follows: $\dfrac{1}{(6)(3)-(9)(-8)}\begin{bmatrix} 3 & -9 \\ 8 & 6 \end{bmatrix} $ This yields to: $\begin{bmatrix} \frac{1}{30} & -\frac{1}{10} \\ \frac{4}{45} & \frac{3}{45} \end{bmatrix} $ Therefore, the value of $x,y$ can be calculated as: $\begin{bmatrix} x \\ y \end{bmatrix}=\begin{bmatrix} \frac{1}{30} & -\frac{1}{10} \\ \frac{4}{45} & \frac{3}{45} \end{bmatrix} \begin{bmatrix} 3 \\ 6 \end{bmatrix} $ After matrix multiplication, we get: $\begin{bmatrix} x \\ y \end{bmatrix}= \begin{bmatrix} -\frac{1}{2} \\ \frac{2}{3} \end{bmatrix} $ Hence, our result is: $\begin{bmatrix} x \\ y \end{bmatrix}= \begin{bmatrix} -\frac{1}{2} \\ \frac{2}{3} \end{bmatrix} $
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