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Ответ:

Вычислить определители .

[tex]\bf 1)\ \ \left|\begin{array}{ccc}\bf 10&\bf 2\\\bf 3&\bf -4\end{array}\right|=10\cdot (-4)-3\cdot 2=-40-6=-46[/tex]  

2) Раскрываем определитель по 1 cтроке .

[tex]\left|\begin{array}{ccc}\bf 1&\bf 2&\bf 3\\\bf 2&\bf 3&\bf 1\\\bf 3&\bf 1&\bf 9\end{array}\right|=1\cdot \left|\begin{array}{ccc}\bf 3&\bf 1\\\bf 1&\bf 9\end{array}\right|-2\cdot \left|\begin{array}{ccc}\bf 2&\bf 1\\\bf 3&\bf 9\end{array}\right|+3\cdot \left|\begin{array}{ccc}\bf 2&\bf 3\\\bf 3&\bf 1\end{array}\right|=\\\\\\\bf =(27-1)-2\cdot (18-3)+3\cdot (2-9)=26-2\cdot 15+3\cdot (-7)=\\\\=26-30-21=-25[/tex]