Với \(a = -7, b = 4,\) ta có:
\(a)\, {a^2} + 2.a.b + {b^2}\)
\(={\left( { - 7} \right)^2} + 2.\left( { - 7} \right).4 + {4^2}\)
\(=49 - 56 + 16 = 9\)
\(\left( {a + b} \right).\left( {a + b} \right)\)
\(=\left[ {\left( { - 7} \right) + 4} \right].\left[ {\left( { - 7} \right) + 4} \right] \)
\(=\left( { - 3} \right).\left( { - 3} \right) = 9\)
\(b)\,{a^2} - {b^2} \)
\(= {\left( { - 7} \right)^2} - {4^2} = 49 - 16 = 33\)
\(\left( {a + b} \right).\left( {a - b} \right)\)
\(= \left[ {\left( { - 7} \right) + 4} \right].\left[ {\left( { - 7} \right) - 4} \right]\)
\(=\left( { - 3} \right).\left( { - 11} \right) = 33\)
