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