I know how to prove the Gerschgorin Theorem but how exactly would one show that there are no values of $\mu$ s.t. $\mu<0$ for which $A-\mu B$ is singular where
$$ A= \begin{bmatrix} 2 & -2 & 0 \\ -3 & 5 & 0 \\ 1 & 2 & 3 \\ \end{bmatrix} $$ and
$$ B= \begin{bmatrix} 2 & 0 & 0 \\ 0 & 2 & 1 \\ 0 & 1 & 2 \\ \end{bmatrix} $$