\[x^{3} - 3x^{2} + 4x - 12 = 0\]
\[x^{2}(x - 3) + 4(x - 3) = 0\]
\[(x - 3)\left( x^{2} + 4 \right) = 0\]
\[x - 3 = 0\ \ \ \ \ \ \ \ x^{2} + 4 = 0\]
\[x = 3\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x^{2} = - 4\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ нет\ корней\]
\[Ответ:x = 3.\]