Đáp án:
$\begin{array}{l}
3{x^4} - 6{x^3} - 15{x^2} + 22x - 12 = 0\\
\Rightarrow 3{x^4} - 9{x^3} + 3{x^3} - 9{x^2} - 6{x^2} + 18x + 4x - 12 = 0\\
\Rightarrow 3{x^3}\left( {x - 3} \right) + 3{x^2}\left( {x - 3} \right) - 6x\left( {x - 3} \right) + 4\left( {x - 3} \right) = 0\\
\Rightarrow \left( {x - 3} \right)\left( {3{x^3} + 3{x^2} - 6x + 4} \right) = 0\\
\Rightarrow \left[ \begin{array}{l}
x = 3\\
3{x^3} + 3{x^2} - 6x + 4 = 0
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
x = 3\\
x = - 2,19
\end{array} \right.
\end{array}$
