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Câu hỏi: Nếu $\int\limits_{1}^{4}{f\left( x \right)\text{d}x=3}$ thì $\int\limits_{1}^{4}{\left[ \dfrac{1}{3}f\left( x \right)-5 \right]\text{d}x}$ bằng
A. $-15$.
B. $-12$.
C. $-14$.
D. $-4$.
A. $-15$.
B. $-12$.
C. $-14$.
D. $-4$.
Ta có $\int\limits_{1}^{4}{\left[ \dfrac{1}{3}f\left( x \right)-5 \right]\text{d}x}=\dfrac{1}{3}\int\limits_{1}^{4}{f\left( x \right)\text{d}x}-5\int\limits_{1}^{4}{\text{d}x}=\dfrac{1}{3}.3-\left. 5x \right|_{1}^{4}=-14$.
Đáp án C.