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: 39

Answer

$\begin{bmatrix} x \\ y \end{bmatrix}= \begin{bmatrix} -2 \\ \frac{3}{4} \end{bmatrix} $

Work Step by Step

We will write the system of equations as follows: $\begin{bmatrix} 3 & 4 \\ -5 & 8 \end{bmatrix} \begin{bmatrix} x \\ y \end{bmatrix}=\begin{bmatrix} -3 \\ 16 \end{bmatrix} $ Next, we will find the inverse of the left matrix factor as follows: $\dfrac{1}{(3)(8)-(4)(-5)}\begin{bmatrix} 8 & -4 \\ 5 & 3 \end{bmatrix} $ This yields to: $\begin{bmatrix} \frac{2}{11} & \frac{-1}{11} \\ \frac{5}{44} & \frac{3}{44} \end{bmatrix} $ Therefore, the value of $x,y$ can be calculated as: $\begin{bmatrix} x \\ y \end{bmatrix}=\begin{bmatrix} \frac{2}{11} & \frac{-1}{11} \\ \frac{5}{44} & \frac{3}{44} \end{bmatrix} \begin{bmatrix} -3 \\ 16 \end{bmatrix} $ After matrix multiplication, we get: $\begin{bmatrix} x \\ y \end{bmatrix}=\begin {bmatrix} \frac{2}{11} (-3)-\frac{1}{11} (16) \\ \frac{5}{44}(-3)+ \frac{3}{44} (16)\end{bmatrix} = \begin{bmatrix} -2 \\ 3/4 \end{bmatrix} $ Hence, our result is: $\begin{bmatrix} x \\ y \end{bmatrix}= \begin{bmatrix} -2 \\ \frac{3}{4} \end{bmatrix} $
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