Cho số thực dương a. Hãy rút gọn các biểu thức sau (giả sử mỗi biểu thức đều có nghĩa):
a) \(\frac{{{a^{\frac{4}{3}}}\left( {{a^{ - \frac{1}{3}}} + {a^{\frac{2}{3}}}} \right)}}{{{a^{\frac{1}{4}}}\left( {{a^{\frac{3}{4}}} + {a^{ - \frac{1}{4}}}} \right)}}\)
b) \(\frac{{{a^{\frac{1}{5}}}\left( {\sqrt[5]{{{a^4}}} - \sqrt[5]{{{a^{ - 1}}}}} \right)}}{{{a^{\frac{2}{3}}}\left( {\sqrt[3]{a} - \sqrt[3]{{{a^{ - 2}}}}} \right)}}\)
Áp dụng: \(\sqrt[n]{{{a^m}}} = {a^{\frac{m}{n}}};{a^n}.{a^m} = {a^{n + m}}\)
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a)
\(\begin{array}{l}\frac{{{a^{\frac{4}{3}}}\left( {{a^{ - \frac{1}{3}}} + {a^{\frac{2}{3}}}} \right)}}{{{a^{\frac{1}{4}}}\left( {{a^{\frac{3}{4}}} + {a^{ - \frac{1}{4}}}} \right)}} = \frac{{{a^{\frac{4}{3}}}.{a^{ - \frac{1}{3}}} + {a^{\frac{4}{3}}}.{a^{\frac{2}{3}}}}}{{{a^{\frac{1}{4}}}.{a^{\frac{3}{4}}} + {a^{\frac{1}{4}}}.{a^{ - \frac{1}{4}}}}}\\ = \frac{{{a^1} + {a^2}}}{{{a^1} + {a^0}}} = \frac{{a + {a^2}}}{{a + 1}} = \frac{{a\left( {a + 1} \right)}}{{a + 1}} = a\end{array}\)
b)
\(\begin{array}{l}\frac{{{a^{\frac{1}{5}}}\left( {\sqrt[5]{{{a^4}}} - \sqrt[5]{{{a^{ - 1}}}}} \right)}}{{{a^{\frac{2}{3}}}\left( {\sqrt[3]{a} - \sqrt[3]{{{a^{ - 2}}}}} \right)}} = \frac{{{a^{\frac{1}{5}}}.{a^{\frac{4}{5}}} - {a^{\frac{1}{5}}}.{a^{\frac{{ - 1}}{5}}}}}{{{a^{\frac{2}{3}}}.{a^{\frac{1}{3}}} - {a^{\frac{2}{3}}}.{a^{\frac{{ - 2}}{3}}}}}\\ = \frac{{{a^1} - {a^0}}}{{{a^1} - {a^0}}} = \frac{{a - 1}}{{a - 1}} = 1\end{array}\)