$解：(2)由题意得，6x-0+12-3(3x-1)=6$
$解得，x=3$
$(3)\left | {{{\begin{pmatrix} {{a}}&{d} \\ {b}&{c} \end{pmatrix}}}} \right |+\left | {{{\begin{pmatrix} {{d}}&{a} \\ {c}&{b} \end{pmatrix}}}} \right |=0，理由：$
$因为\left | {{{\begin{pmatrix} {{a}}&{d} \\ {b}&{c} \end{pmatrix}}}} \right |=ac-bd，\left | {{{\begin{pmatrix} {{d}}&{a} \\ {c}&{b} \end{pmatrix}}}} \right |=bd-ac，$
$所以\left | {{{\begin{pmatrix} {{a}}&{d} \\ {b}&{c} \end{pmatrix}}}} \right |+\left | {{{\begin{pmatrix} {{d}}&{a} \\ {c}&{b} \end{pmatrix}}}} \right |=ac-bd+bd-ac=0$
$(4)\left | {{{\begin{pmatrix} {{2}}&{2} \\ {4}&{3} \end{pmatrix}}}} \right |$
