Đáp án:
$\begin{array}{l}
{\left( {\dfrac{7}{{{2^9}}} - \dfrac{{14}}{{{2^{11}}}} + \dfrac{{21}}{{768}}} \right)^2}:{\left( {\dfrac{5}{{{2^9}}} - \dfrac{{20}}{{{2^{12}}}} + \dfrac{{25}}{{1280}}} \right)^2}\\
= {\left( {\dfrac{7}{{{2^9}}} - \dfrac{7}{{{2^{10}}}} + \dfrac{7}{{256}}} \right)^2}:{\left( {\dfrac{5}{{{2^9}}} - \dfrac{5}{{{2^{10}}}} + \dfrac{5}{{256}}} \right)^2}\\
= {7^2}.{\left( {\dfrac{1}{{{2^9}}} - \dfrac{1}{{{2^{10}}}} + \dfrac{1}{{256}}} \right)^2}:\left[ {{5^2}.{{\left( {\dfrac{1}{{{2^9}}} - \dfrac{1}{{{2^{10}}}} + \dfrac{1}{{256}}} \right)}^2}} \right]\\
= {7^2}:{5^2}\\
= \dfrac{{49}}{{25}}
\end{array}$
