Đề bài

Cho \(a > 0;a \ne 1;{a^{\frac{3}{5}}} = b\) a)     Viết \({a^6};{a^3}b;\frac{{{a^9}}}{{{b^9}}}\) theo lũy thừa cơ số b b)    Tính \({\log _a}b;\,{\log _a}\left( {{a^2}{b^5}} \right);\,{\log _{\sqrt[5]{a}}}\left( {\frac{a}{b}} \right)\)

Lời giải chi tiết

a)     \({a^6} = {a^{\frac{{30}}{5}}} = {\left( {{a^{\frac{3}{5}}}} \right)^{10}} = {b^{10}}\)\({a^3}b = {a^{\frac{{15}}{5}}}b = {\left( {{a^{\frac{3}{5}}}} \right)^5}b = {b^5}.b = {b^6}\)\(\left( {\frac{{{a^9}}}{{{b^9}}}} \right) = {\left( {\frac{a}{b}} \right)^9} = {\left( {\frac{a}{{{a^{\frac{3}{5}}}}}} \right)^9} = {\left( {{a^{\frac{2}{5}}}} \right)^9} = {a^{\frac{{18}}{5}}} = {\left( {{a^{\frac{3}{5}}}} \right)^6} = {b^6}\)b)    \({\log _a}b = {\log _a}{a^{\frac{3}{5}}} = \frac{3}{5}\)\({\log _a}\left( {{a^2}{b^5}} \right) = {\log _a}\left( {{a^2}.{{\left( {{a^{\frac{3}{5}}}} \right)}^5}} \right) = {\log _a}\left( {{a^2}.{a^3}} \right) = {\log _a}\left( {{a^5}} \right) = 5\)\({\log _{\sqrt[5]{a}}}\left( {\frac{a}{b}} \right) = {\log _{{a^{\frac{1}{5}}}}}\left( {\frac{a}{{{a^{\frac{3}{5}}}}}} \right) = 5{\log _a}{a^{\frac{2}{5}}} = 2\)