Been a while since I had to do this... totally forgot how to <_<

the only thing I can remember is $\displaystyle A^{-1} = \frac{1}{ad-bc} * \left(\begin{array}{cc}d&-b\\-c&a\end{array}\right)$ or something...

But this leaves me absolutely clueless on how to solve

$\displaystyle A^{-1} = \left(\begin{array}{ccc}1&2&3\\2&3&4\\3&4&6\end{ar ray}\right)$

Thx in advance!