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