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Câu hỏi: Nếu $\int\limits_{1}^{2}{f\left( x \right)\text{d}x=2}$ thì $\int\limits_{1}^{2}{\left[ f\left( x \right)+2x \right]\text{d}x}$ bằng
A. $3$.
B. $4$.
C. $5$.
D. $1$.
A. $3$.
B. $4$.
C. $5$.
D. $1$.
Ta có: $\int\limits_{1}^{2}{\left[ f\left( x \right)+2x \right]\text{d}x}=\int\limits_{1}^{2}{f\left( x \right)\text{d}x}+\int\limits_{1}^{2}{2x\text{d}x}=2+\left. {{x}^{2}} \right|_{1}^{2}=2+\left( 4-1 \right)=5$.
Đáp án C.