Rút gọn biểu thức ( 7/ 2 mũ 9 – 14/2 mũ 11+21/768)mũ 2 : ( 5/2 mũ 9 – 20/2 mũ 12 + 25/1280) mũ 2

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1. Đáp án:

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

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