Đáp án:
$\begin{array}{l}
a)a.x + a.y - 3x - 3y\\
= a.\left( {x + y} \right) - 3.\left( {x + y} \right)\\
= \left( {x + y} \right)\left( {a - 3} \right)\\
b)xy + 1 - x - y\\
= \left( {xy - x} \right) - \left( {y - 1} \right)\\
= x.\left( {y - 1} \right) - \left( {y - 1} \right)\\
= \left( {y - 1} \right)\left( {x - 1} \right)\\
c){x^3} - 2{x^2} + 2x - 4\\
= {x^2}\left( {x - 2} \right) + 2\left( {x - 2} \right)\\
= \left( {x - 2} \right)\left( {{x^2} + 2} \right)\\
d){x^2} + a.b + a.x + b.x\\
= \left( {{x^2} + a.x} \right) + \left( {ab + b.x} \right)\\
= x\left( {x + a} \right) + b\left( {a + x} \right)\\
= \left( {x + a} \right)\left( {x + b} \right)\\
e)xy - 4 + 2x - 2y\\
= \left( {xy + 2x} \right) - \left( {2y + 4} \right)\\
= x.\left( {y + 2} \right) - 2\left( {y + 2} \right)\\
= \left( {y + 2} \right)\left( {x - 2} \right)\\
g)a.x + b.x - c.x + a + b - c\\
= x.\left( {a + b - c} \right) + \left( {a + b - c} \right)\\
= \left( {a + b - c} \right)\left( {x + 1} \right)
\end{array}$
