Đáp án
$\begin{array}{l}
5{x^4} + 3{x^3}y - 20{x^2}{y^2} - 12x{y^3}\\
= x\left( {5{x^3} + 3{x^2}y - 20x{y^2} - 12{y^3}} \right)\\
= x.\left( {{x^2}\left( {5x + 3y} \right) - 4{y^2}\left( {5x + 3y} \right)} \right)\\
= x.\left( {5x + 3y} \right)\left( {{x^2} - 4{y^2}} \right)\\
= x.\left( {5x + 3y} \right)\left( {x + 2y} \right)\left( {x - 2y} \right)
\end{array}$