Đáp án:
$\begin{array}{l}
{\left( {2x + 3} \right)^2} + {\left( {2x - 3} \right)^2} - \left( {2x + 3} \right)\left( {4x - 6} \right) + xy\\
= {\left( {2x + 3} \right)^2} - 2.\left( {2x + 3} \right).\left( {2x - 3} \right) + {\left( {2x - 3} \right)^2} + xy\\
= {\left( {2x + 3 - 2x + 3} \right)^2} + xy\\
= {6^2} + xy\\
= xy + 36\\
\left( {4{x^2} + 4x + 1} \right):\left( {2x + 1} \right)\\
= {\left( {2x + 1} \right)^2}:\left( {2x + 1} \right)\\
= 2x + 1
\end{array}$