Câu hỏi: Nếu $\int\limits_{1}^{4}{f\left( x \right)\text{d}x}=6$ thì $\int\limits_{1}^{4}{2f\left( x \right)\text{d}x}$ bằng A. $3$. B. $4$. C. $12$. D. $8$.
Ta có $\int\limits_{1}^{4}{2f\left( x \right)\text{d}x}=2\cdot \int\limits_{1}^{4}{f\left( x \right)\text{d}x}=2\cdot 6=12$.