Answer
$\left[\begin{array}{ll}
1 & 0\\
0 & 1
\end{array}\right]$
(sample answer)
Work Step by Step
If $A=\left[\begin{array}{ll}
a & b\\
c & d
\end{array}\right]$, then$ A$ is invertible if and only if $ad-bc\neq 0$,
and,
$A^{-1}=\displaystyle \frac{1}{ad-bc}\left[\begin{array}{ll}
d & -b\\
-c & a
\end{array}\right]$.
---------
Since $I\cdot I=I,$
the simplest example is
$\left[\begin{array}{ll}
1 & 0\\
0 & 1
\end{array}\right].$
$I^{-1}=\displaystyle \frac{1}{1(1)-0}\left[\begin{array}{ll}
1 & -0\\
-0 & 1
\end{array}\right]=\displaystyle \left[\begin{array}{ll}
1 & 0\\
0 & 1
\end{array}\right]=I$.
