$解：(2)由題意得，6x-0+12-3(3x-1)=6$
$解得，x=3$
$(3)\left | {{{\begin{pmatrix} {{a}}&h8xf99z8w \\ &{c} \end{pmatrix}}}} \right |+\left | {{{\begin{pmatrix} {h8xf99z8w}&{a} \\ {c}& \end{pmatrix}}}} \right |=0，理由：$
$因為\left | {{{\begin{pmatrix} {{a}}&h8xf99z8w \\ &{c} \end{pmatrix}}}} \right |=ac-bd，\left | {{{\begin{pmatrix} {h8xf99z8w}&{a} \\ {c}& \end{pmatrix}}}} \right |=bd-ac，$
$所以\left | {{{\begin{pmatrix} {{a}}&h8xf99z8w \\ &{c} \end{pmatrix}}}} \right |+\left | {{{\begin{pmatrix} {h8xf99z8w}&{a} \\ {c}& \end{pmatrix}}}} \right |=ac-bd+bd-ac=0$
$(4)\left | {{{\begin{pmatrix} {{2}}&{2} \\ {4}&{3} \end{pmatrix}}}} \right |$
