College Algebra (6th Edition)

Published by Pearson
ISBN 10: 0-32178-228-3
ISBN 13: 978-0-32178-228-1

Chapter 6 - Matrices and Determinants - Exercise Set 6.4 - Page 641: 87

Answer

The statement is false. To make it true, replace the equals sign with "$\neq$".

Work Step by Step

If $A=\left[\begin{array}{ll} a & b\\ c & d \end{array}\right]$, then $A^{-1}=\displaystyle \frac{1}{ad-bc}\left[\begin{array}{ll} d & -b\\ -c & a \end{array}\right]$. --------- Counterexample: Let A=$\left[\begin{array}{ll} 1 & 0\\ 0 & 1 \end{array}\right]$, B=$\left[\begin{array}{ll} 2 & 0\\ 0 & 2 \end{array}\right]$ $A^{-1}=\displaystyle \frac{1}{1(1)-0}\left[\begin{array}{ll} 1 & 0\\ 0 & 1 \end{array}\right]$=$\left[\begin{array}{ll} 1 & 0\\ 0 & 1 \end{array}\right],$ $B^{-1}=\displaystyle \frac{1}{2(2)-0}\left[\begin{array}{ll} 2 & 0\\ 0 & 2 \end{array}\right]=\displaystyle \left[\begin{array}{ll} 1/2 & 0\\ 0 & 1/2 \end{array}\right]$ $A^{-1}+B^{-1}=\left[\begin{array}{ll} 3/2 & 0\\ 0 & 3/2 \end{array}\right]$ On the other hand, $A+B=\left[\begin{array}{ll} 3 & 0\\ 0 & 3 \end{array}\right], and$ $(A+B)^{-1}=\displaystyle \frac{1}{3(3)-0}\left[\begin{array}{ll} 3 & 0\\ 0 & 3 \end{array}\right]=\displaystyle \left[\begin{array}{ll} 1/3 & 0\\ 0 & 1/3 \end{array}\right]$ So, generally, $(A+B)^{-1}\neq A^{-1}+B^{-1}$ The statement is false. To make it true, replace the equals sign with "$\neq$".
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.