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Câu hỏi: Cho a, b là các số thực dương, $a\ne 1$. Đẳng thức nào dưới đây đúng?
A. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3-2{{\log }_{a}}b$.
B. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3+2{{\log }_{a}}b$.
C. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3-\dfrac{1}{2}{{\log }_{a}}b$.
D. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3+\dfrac{1}{2}{{\log }_{a}}b$.
A. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3-2{{\log }_{a}}b$.
B. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3+2{{\log }_{a}}b$.
C. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3-\dfrac{1}{2}{{\log }_{a}}b$.
D. ${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)=3+\dfrac{1}{2}{{\log }_{a}}b$.
${{\log }_{a}}\left( \dfrac{{{a}^{3}}}{\sqrt{b}} \right)={{\log }_{a}}{{a}^{3}}-{{\log }_{a}}\sqrt{b}=3-\dfrac{1}{2}{{\log }_{a}}b$
Đáp án C.