Đáp án:
$\begin{array}{l}
C1:\\
2{x^2} - 6xy + 5x - 15y\\
= 2x.\left( {x - 3y} \right) + 5.\left( {x - 3y} \right)\\
= \left( {x - 3y} \right)\left( {2x + 5} \right)\\
C2:\\
2{x^2} - 6xy + 5x - 15y\\
= 2{x^2} + 5x - 6xy - 15y\\
= x\left( {2x + 5} \right) - 3y\left( {2x + 5} \right)\\
= \left( {2x + 5} \right)\left( {x - 3y} \right)
\end{array}$