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 732: 11

Answer

$A^{-1}=\left[\begin{array}{rr} 3 & 5\\ -2 & -3 \end{array}\right]$

Work Step by Step

$A=\displaystyle \left[\begin{array}{ll} a & b\\ c & d \end{array}\right] \Rightarrow A^{-1}=\frac{1}{ad-bc}\left[\begin{array}{ll} d & -b\\ -c & a \end{array}\right]$ ($A^{-1}$ exists if and only if $ad-bc\neq 0)$ ---- $\left[\begin{array}{ll} a & b\\ c & d \end{array}\right]=\left[\begin{array}{ll} -3 & -5\\ 2 & 3 \end{array}\right]$ $ad-bc=-3(3)-(-5)(2)=1\neq 0$ $A^{-1}=(1)\cdot\left[\begin{array}{ll} 3 & 5\\ -2 & -3 \end{array}\right]$ $A^{-1}=\left[\begin{array}{ll} 3 & 5\\ -2 & -3 \end{array}\right]$
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