Resposta :
[tex]A = \left(\begin{array}{ccc}a_{11}&a_{12}\\a_{21}&a_{22}\end{array}\right) \\\\\\ a_{11} \Rightarrow i=j \Rightarrow a_{11} = 1 \\\\ a_{12} \Rightarrow i \neq j \Rightarrow a_{12} = 2 \\\\ a_{21} \Rightarrow i \neq j \Rightarrow a_{21} = 1 \\\\ a_{22} \Rightarrow i = j \Rightarrow a_{22} = 2 \\\\\\ A = \left(\begin{array}{ccc}1&2\\1&2\end{array}\right)[/tex]