a
$\left| {\begin{array}{*{20}{c}} { - 2}&{ - 2}&0 \\ 2&0&{ - 1} \\ {{{\sin }^2}x}&{{{\cos }^2}x}&{1 + \cos 2x} \end{array}} \right| (\mathrm{R}_{1} \rightarrow \mathrm{R}_{1}-\mathrm{R}_{2} \,and \,\mathrm{R}_{2} \rightarrow \mathrm{R}_{2}-\mathrm{R}_{3})$
$-2\left(\cos ^{2} \mathrm{x}\right)+2\left(2+2 \cos 2 \mathrm{x}+\sin ^{2} \mathrm{x}\right)$
$4+4 \cos 2 \mathrm{x}-2\left(\cos ^{2} \mathrm{x}-\sin ^{2} \mathrm{x}\right)$
$\mathrm{f}(\mathrm{x})=4+\underbrace{2 \cos 2 \mathrm{x}}_{\max =1}$
$\mathrm{f}(\mathrm{x})_{\max }=4+2=6$