Đáp án:
$\begin{array}{l}
a)4{x^2} - 12x - {y^2} + 2y + 8\\
= 4{x^2} - 2.2x.3 + 9 - {y^2} + 2y - 1\\
= {\left( {2x - 3} \right)^2} - {\left( {y - 1} \right)^2}\\
c)\left( {x + y + 4} \right)\left( {x + y - 4} \right)\\
= {\left( {x + y} \right)^2} - {4^2}\\
d)\left( {x - y + 6} \right)\left( {x + y - 6} \right)\\
= {x^2} - {\left( {y - 6} \right)^2}\\
e)\left( {y + 2z + 3} \right)\left( {y - 2z - 3} \right)\\
= {y^2} - {\left( {2z + 3} \right)^2}\\
f)\left( {x + 2y + 3z} \right)\left( {2y + 3z - x} \right)\\
= {\left( {2y + 3z} \right)^2} - {x^2}
\end{array}$
Câu b đề sai