Đáp án:
$\begin{array}{l}
B = {\left( {x + y} \right)^2} + 3\left( {x + y} \right) + 2\\
= {\left( {x + y} \right)^2} + 2\left( {x + y} \right) + \left( {x + y} \right) + 2\\
= \left( {x + y} \right)\left( {x + y + 2} \right) + \left( {x + y + 2} \right)\\
= \left( {x + y + 2} \right)\left( {x + y} \right)
\end{array}$