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Câu hỏi: Tính $\int_0^1 3^{2 x+1} \mathrm{~d} x$ bằng
A. $\dfrac{12}{\ln 3}$.
B. $\dfrac{4}{\ln 3}$.
C. $\dfrac{27}{\ln 9}$.
D. $\dfrac{9}{\ln 9}$.
A. $\dfrac{12}{\ln 3}$.
B. $\dfrac{4}{\ln 3}$.
C. $\dfrac{27}{\ln 9}$.
D. $\dfrac{9}{\ln 9}$.
Ta có $\int_0^1 3^{2 x+1} \mathrm{~d} x=\left.\dfrac{1}{2} \cdot \dfrac{3^{2 x+1}}{\ln 3}\right|_0 ^1=\dfrac{1}{2 \ln 3}\left(3^3-3\right)=\dfrac{12}{\ln 3}$.
Đáp án A.