Đáp án:
$\begin{array}{l}
A = {81^{\frac{1}{4}}} - \frac{1}{2}{\log _9}4 + {20^{{{\log }_{125}}8}}\\
= \sqrt[4]{{81}} - \frac{1}{2}.{\log _{{3^2}}}{.2^2} + {20^{{{\log }_{{5^3}}}{2^3}}}\\
= 3 - \frac{1}{2}.{\log _3}2 + {20^{{{\log }_5}2}}\\
= 3 - \frac{1}{2}.{\log _3}2 + {2^{{{\log }_5}20}}\\
= 3 - \frac{1}{2}.{\log _3}2 + {2^{{{\log }_5}\left( {{2^2}.5} \right)}}\\
= 3 - \frac{1}{2}.{\log _3}2 + {2^{1 + 2{{\log }_5}2}}\\
= 3 - \frac{1}{2}.{\log _3}2 + 2.1,816\\
= 6,318
\end{array}$
(Lần sau bạn ghi rõ đề ra nhé)
