# Math Help - matrix algebra

1. ## matrix algebra

for the square matrix A can
(I + A)^-1 be expanded or simplified. is it true (I + A)^-1 = A^-1 - I
where I is the identity matrix
thanks to anyone who can help

2. Originally Posted by smiler
for the square matrix A can
(I + A)^-1 be expanded or simplified. is it true (I + A)^-1 = A^-1 - I
where I is the identity matrix
thanks to anyone who can help
No, it is not true. (It's not even true for scalars.)
Consider:
$A = \left ( \begin{matrix} 1 & 9 \\ -4 &2 \end{matrix} \right )$
(I just randomly selected numbers here. It is not a "special" case.)

You'll see that it doesn't work out.

-Dan