Trong mỗi trường hợp sau, hãy tìm x:
a) \({\log _3}x = 4{\log _3}a + 7{\log _3}b\)
b) \({\log _5}x{\rm{ }} = {\rm{ }}2{\log _5}a{\rm{ }} - {\rm{ }}3{\log _5}b\)
a)
\(\begin{array}{l}
{\log _3}x = 4{\log _3}a + 7{\log _3}b\\
= {\log _3}{a^4} + {\log _3}{b^7}\\
= {\log _3}\left( {{a^4}{b^7}} \right) \Rightarrow x = {a^4}{b^7}
\end{array}\)
b)
\(\begin{array}{l}
{\log _5}x = 2{\log _5}a - 3{\log _5}b\\
= {\log _5}\frac{{{a^2}}}{{{b^3}}} \Rightarrow x = \frac{{{a^2}}}{{{b^3}}}.
\end{array}\)
-- Mod Toán 12
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