Đáp án:
$\begin{array}{l}
a)2{x^3} + 3{x^2} - x - 1\\
= 2{x^3} + {x^2} + 2{x^2} + x - 2x - 1\\
= {x^2}\left( {2x + 1} \right) + x\left( {2x + 1} \right) - \left( {2x + 1} \right)\\
= \left( {2x + 1} \right)\left( {{x^2} + x - 1} \right)\\
b)3{x^3} - 5{x^2} - x + 2\\
= 3{x^3} - 2{x^2} - 3{x^2} + 2x - 3x + 2\\
= {x^2}\left( {3x - 2} \right) - x\left( {3x - 2} \right) - \left( {3x - 2} \right)\\
= \left( {3x - 2} \right)\left( {{x^2} - x - 1} \right)\\
c)2{x^3} - {x^2} + 3x + 2\\
= 2{x^3} + {x^2} - 2{x^2} - x + 4x + 2\\
= {x^2}\left( {2x + 1} \right) - x\left( {2x + 1} \right) + 2\left( {2x + 1} \right)\\
= \left( {2x + 1} \right)\left( {{x^2} - x + 2} \right)
\end{array}$
(ý d bị lẻ, có thể là sai đề)