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Câu hỏi: Nếu $\int_{1}^{3}{f\left( x \right)\text{d}x}=2$ thì $\int_{1}^{3}{\left[ f\left( x \right)+2x \right]\text{d}x}$ bằng
A. $12$.
B. $18$.
C. $10$.
D. $20$.
A. $12$.
B. $18$.
C. $10$.
D. $20$.
$\int_{1}^{3}{\left[ f\left( x \right)+2x \right]\text{d}x}=\int_{1}^{3}{f\left( x \right)\text{d}x+\int_{1}^{3}{2x\text{d}x}}=2+8=10$.
Đáp án C.