Đáp án:
$\begin{array}{l}
1)5{x^2}{y^2} + 20{x^2}y - 35x{y^2}\\
= 5xy\left( {xy + 4x - 7y} \right)\\
2)40{a^3}{b^3}{c^3} + 120{a^3}{b^4}{c^2} - 16{a^4}{b^5}cx\\
= 8{a^3}{b^3}c\left( {5{c^2} + 15bc - 2a{b^2}x} \right)\\
3)2{x^3}{y^4} - 6{x^4}{y^3} + 4{x^2}{y^2}\\
= 2{x^2}{y^2}\left( {x{y^2} - 3{x^2}y + 2} \right)\\
4){\left( {2x - 5y} \right)^2} - 4\left( {2x - 5y} \right)\\
= \left( {2x - 5y} \right)\left( {2x - 5y - 4} \right)\\
5)3x\left( {x - 2y} \right) + 6y\left( {2y - x} \right)\\
= 3x\left( {x - 2y} \right) - 6y\left( {x - 2y} \right)\\
= 3\left( {x - 2y} \right)\left( {x - 2y} \right)\\
= 3{\left( {x - 2y} \right)^2}\\
6)\left( {b - 2c} \right)\left( {a - b} \right) - \left( {a + b} \right)\left( {2c - b} \right)\\
= \left( {b - 2c} \right)\left( {a - b} \right) + \left( {a + b} \right)\left( {b - 2c} \right)\\
= \left( {b - 2c} \right)\left( {a - b + a + b} \right)\\
= 2a\left( {b - 2c} \right)\\
7)6\left( {a - b} \right){x^2}y + {\left( {a - b} \right)^2}xy\\
= \left( {a - b} \right)xy\left( {6x + a - b} \right)
\end{array}$
