Lời giải

Đáp án đúng là: A

\[\frac{{{\rm{x + 3}}}}{{{{\rm{x}}^{\rm{2}}} - {\rm{4}}}}{\rm{.}}\frac{{{\rm{8}} - {\rm{12x + 6}}{{\rm{x}}^{\rm{2}}} - {{\rm{x}}^{\rm{3}}}}}{{{\rm{9x + 27}}}}\]

\[{\rm{ = }}\frac{{{\rm{x + 3}}}}{{\left( {{\rm{x}} - {\rm{2}}} \right)\left( {{\rm{x + 2}}} \right)}}{\rm{.}}\frac{{{{\left( {{\rm{2}} - {\rm{x}}} \right)}^{\rm{3}}}}}{{{\rm{9}}\left( {{\rm{x + 3}}} \right)}}\]

\[{\rm{ = }} - \frac{{{{\left( {{\rm{x}} - {\rm{2}}} \right)}^{\rm{2}}}}}{{{\rm{9}}\left( {{\rm{x + 2}}} \right)}}\].

Vậy\[{\rm{A = }}{\left( {{\rm{x}} - {\rm{2}}} \right)^{\rm{2}}}{\rm{;}}\,\,{\rm{B = 9}}\left( {{\rm{x + 2}}} \right)\].