b
(b) $A = \left[ {\begin{array}{*{20}{c}}1&2&0\\0&1&2\\2&0&1\end{array}} \right]$,
${A_{11}} = 1,\,{A_{21}} = - 2,\,{A_{31}} = 4$
${A_{12}} = 4,\,{A_{22}} = 1,\,{A_{32}} = - 2$
${A_{13}} = - 2,\,{A_{23}} = 4,\,{A_{33}} = 1$
$Adj\,(A) = \left[ {\begin{array}{*{20}{c}}1&{ - 2}&4\\4&1&{ - 2}\\{ - 2}&4&1\end{array}} \right]$.