Rút gọn biểu thức: \(\sqrt {\dfrac{m}{{1 - 2x + {x^2}}}} .\sqrt {\dfrac{{4m - 8mx + 4m{x^2}}}{{81}}} \)

* Hướng dẫn giải

 \(\sqrt {\dfrac{m}{{1 - 2x + {x^2}}}} .\sqrt {\dfrac{{4m - 8mx + 4m{x^2}}}{{81}}}\)

\( = \sqrt {\dfrac{m}{{{{\left( {1 - x} \right)}^2}}}} \sqrt {\dfrac{{4m\left( {1 - 2x + {x^2}} \right)}}{{81}}}\)

\(= \sqrt {\dfrac{{{2^2}{m^2}{{\left( {1 - x} \right)}^2}}}{{{{\left( {1 - x} \right)}^2}{{.9}^2}}}}\)

\(= \dfrac{{\left| {2m} \right|}}{9} = \dfrac{{2m}}{9}\)