Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 10 - Section 10.5 - Inverses of Matrices and Matrix Questions - 10.5 Exercises - Page 731: 2

Answer

$a.\qquad\left[\begin{array}{ll} 5 & 3\\ 3 & 2 \end{array}\right]\cdot\left[\begin{array}{l} x\\ y \end{array}\right]=\left[\begin{array}{l} 4\\ 3 \end{array}\right]$ $b.\qquad A^{-1}=\left[\begin{array}{ll} 2 & -3\\ -3 & 5 \end{array}\right]$ $c.\qquad\left[\begin{array}{l} x\\ y \end{array}\right]=\left[\begin{array}{ll} 2 & -3\\ -3 & 5 \end{array}\right]\left[\begin{array}{l} 4\\ 3 \end{array}\right]=\left[\begin{array}{l} -1\\ 3 \end{array}\right]$ $d.\qquad x=-1,\qquad y=3$

Work Step by Step

$a.$ $A\cdot X=B$ $\left[\begin{array}{ll} 5 & 3\\ 3 & 2 \end{array}\right]\cdot\left[\begin{array}{l} x\\ y \end{array}\right]=\left[\begin{array}{l} 4\\ 3 \end{array}\right]$ $(b)$ $A=\displaystyle \left[\begin{array}{ll} a & b\\ c & d \end{array}\right] \Rightarrow A^{-1}=\frac{1}{ad-bc}\left[\begin{array}{ll} d & -b\\ -c & a \end{array}\right]$ $A^{-1}=\displaystyle \frac{1}{5(2)-3(3)}\left[\begin{array}{ll} 2 & -3\\ -3 & 5 \end{array}\right]$ $A^{-1}=\displaystyle \frac{1}{1}\left[\begin{array}{ll} 2 & -3\\ -3 & 5 \end{array}\right]$ $A^{-1}=\left[\begin{array}{ll} 2 & -3\\ -3 & 5 \end{array}\right]$ $(c)$ $X=A^{-1}B=\left[\begin{array}{ll} 2 & -3\\ -3 & 5 \end{array}\right]\left[\begin{array}{l} 4\\ 3 \end{array}\right]=\left[\begin{array}{l} 2(4)-3(3)\\ -3(4)+5(3) \end{array}\right]=\left[\begin{array}{l} -1\\ 3 \end{array}\right]$ $\left[\begin{array}{l} x\\ y \end{array}\right]=\left[\begin{array}{ll} 2 & -3\\ -3 & 5 \end{array}\right]\left[\begin{array}{l} 4\\ 3 \end{array}\right]=\left[\begin{array}{l} -1\\ 3 \end{array}\right]$ $(d)$ $x=-1,\qquad y=3$
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