Đáp án:
$\begin{array}{l}
a)M = \left( {2a + 3} \right)\left( {2b + 3} \right)\\
= 4ab + 6a + 6b + 9\\
= 4.\left( { - 4} \right) + 6.\left( {a + b} \right) + 9\\
= - 16 + 6.2 + 9\\
= - 16 + 12 + 9\\
= 5\\
b)N = {\left( {a - b} \right)^2}\\
= {a^2} - 2ab + {b^2}\\
= {a^2} + 2ab + {b^2} - 4ab\\
= {\left( {a + b} \right)^2} - 4ab\\
= {2^2} - 4.\left( { - 4} \right)\\
= 4 + 16 = 20\\
c)P = \left( {3a + 2b} \right)\left( {3b + 2a} \right) - 5a - 5b\\
= 9ab + 6{a^2} + 6{b^2} + 4ab - 5\left( {a + b} \right)\\
= 6\left( {{a^2} + {b^2} + 2ab} \right) - 12ab + 13ab - 5\left( {a + b} \right)\\
= 6.{\left( {a + b} \right)^2} + ab - 5\left( {a + b} \right)\\
= {6.2^2} + \left( { - 4} \right) - 5.2\\
= 24 - 4 - 10\\
= 10
\end{array}$
