Elementary Linear Algebra 7th Edition

Published by Cengage Learning
ISBN 10: 1-13311-087-8
ISBN 13: 978-1-13311-087-3

Chapter 2 - Matrices - 2.3 The Inverse of a Matrix - 2.3 Exercises - Page 73: 78

Answer

No

Work Step by Step

No, because the sum of the inverses of the matrices $A$ and $B$ must be invertible and in the following, we indicate the reason Since $A$ and $B$ are invertible matrices, then $A+B=AB^{-1}B+AA^{-1}B=A(B^{-1}+A^{-1})B$ and then $(A+B)^{-1}=(A(B^{-1}+A^{-1})B)^{-1}=((B^{-1}+A^{-1})B)^{-1}A^{-1}=B^{-1} (B^{-1}+A^{-1})^{-1} A^{-1}$ Example :- if $A=I$ and $B=-I $ , then $A^{-1}=I $and $B^{-1}=-I$ , Then $B^{-1}+A^{-1}=O$ and the matrix $B^{-1}+A^{-1}$ is singular , thus in this example the matrix $B^{-1}+A^{-1}$ is not invertible
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