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