\(\begin{array}{l}
Bai\,\,\,\,2:\\
1)\,\,{x^2} + 2x + 1 = {\left( {x + 1} \right)^2}\\
2)\,\,\,{x^2} - 4x + 4 = {\left( {x - 2} \right)^2}\\
3)\,\,\,{x^2} - 14x + 49 = {\left( {x - 7} \right)^2}\\
4)\,\,{x^2} - 6xy + 9{y^2} = {\left( {x - 3y} \right)^2}\\
5)\,\,6)\,\,\,7)\,\,\,lam\,\,tuong\,\,tu.\\
8)\,\,{x^2} - 4 = \left( {x - 2} \right)\left( {x + 2} \right)\\
9)\,\,\,10)\,\,11)\,\,....\,\,\,lam\,\,\,tuong\,\,tu.\\
Bai\,\,3:\\
1)\,\,\,5ax + 5ay + x + y = 5a\left( {x + y} \right) + x + y = \left( {x + y} \right)\left( {5a + 1} \right)\\
2)\,\,2xy - x + 2{y^2} - y = \left( {2xy + 2{y^2}} \right) - \left( {x + y} \right)\\
= 2y\left( {x + y} \right) - \left( {x + y} \right) = \left( {x + y} \right)\left( {2y - 1} \right).\\
3)\,\,ax + bx - ay - by = x\left( {a + b} \right) - y\left( {a + b} \right)\\
= \left( {a + b} \right)\left( {x - y} \right).
\end{array}\)
