If $A^{-1} + B^{-1} =(A+B)^{-1}$ where A and B are non singular n×n matrices with real entries . Prove that $|A|=|B|$

60 Views Asked by At

My attempt : $(A^{-1}+B^{-1})(A+B)=I $ . $A^{-1}B + B^{-1}A=-I . $
$| A^{-1}BA|=|-A-B^{-1}A^{2}. | .$ $|B|=|I + B^{-1}A||A|.$ . I am stuck over here

1

There are 1 best solutions below

0
On BEST ANSWER

$$(A^{-1}+B^{-1})(A+B)=I \\ I+A^{-1}B+B^{-1}A+I=I\\ A^{-1}B+B^{-1}A+I=0 $$

Multiply on the left by $A$ and then by $B$.

$$B+AB^{-1}A+A=0\\ BA^{-1}B+A+B=0$$

This gives $$BA^{-1}B=AB^{-1}A$$

Apply the det and you are done.