b
(b) $\Delta = \left| {\,\begin{array}{*{20}{c}}3&1&1\\0&{ - 1 - {\omega ^2}}&{{\omega ^2}}\\0&{{\omega ^2}}&\omega \end{array}\,} \right|$
$({C_1} \to {C_1} + {C_2} + {C_3})$
$(\because\,\,1 + \omega + {\omega ^2} = 0)$
$ = 3\,[\omega .\omega - {\omega ^4}] = 3({\omega ^2} - \omega )$ $ = 3\omega (\omega - 1)$.