Câu hỏi: Đặt $\text{lo}{{\text{g}}_{2}}3=a,\text{lo}{{\text{g}}_{2}}5=b$. Khi đó $\text{lo}{{\text{g}}_{5}}3$ bằng A. $a-b$. B. $ab$. C. $\dfrac{b}{a}$. D. $\dfrac{a}{b}$.
Ta có $\text{lo}{{\text{g}}_{5}}3=\dfrac{\text{lo}{{\text{g}}_{2}}3}{\text{lo}{{\text{g}}_{2}}5}=\dfrac{a}{b}$.