# Math Help - Inverse Matrix question

1. ## Inverse Matrix question

The matrix I is its own inverse, since I•I=I

1. Find two second order matrices (other than I) that have this property.

2. If A=A^-1, show that det A = +/-1.

Any suggestions? Thanks,

Newt

2. Hello,

Try :
10
01

01
10

3. 2. If A=A^-1, show that det A = +/-1.

Any suggestions? Thanks,

$\left| {A^{ - 1} } \right| = \frac{1}
{{\left| A \right|}}
$

therefore if:
$

\begin{gathered}
\left| A \right| = \frac{1}
{{\left| A \right|}} \hfill \\
\Leftrightarrow \left| A \right|^2 = 1 \hfill \\
\Leftrightarrow \left| A \right| = \pm 1 \hfill \\
\end{gathered}$