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Câu hỏi: Nếu $\int\limits_{0}^{1}{f\left( x \right)\text{d}x}=2$ và $\int\limits_{0}^{1}{\left[ f\left( x \right)-2g\left( x \right) \right]\text{d}x}=-8$ thì $\int\limits_{0}^{1}{g\left( x \right)\text{d}x}$ bằng
A. $-5$.
B. 5.
C. $-6$.
D. $-3$.
Ta có $\int\limits_{0}^{1}{\left[ f\left( x \right)-2g\left( x \right) \right]\text{d}x}=-8$ $\Leftrightarrow \int\limits_{0}^{1}{f\left( x \right)\text{d}x}-2\int\limits_{0}^{1}{g\left( x \right)\text{d}x}=-8$
$\Leftrightarrow 2-2\int\limits_{0}^{1}{g\left( x \right)\text{d}x}=-8$ $\Leftrightarrow \int\limits_{0}^{1}{g\left( x \right)\text{d}x}=5$.
A. $-5$.
B. 5.
C. $-6$.
D. $-3$.
Ta có $\int\limits_{0}^{1}{\left[ f\left( x \right)-2g\left( x \right) \right]\text{d}x}=-8$ $\Leftrightarrow \int\limits_{0}^{1}{f\left( x \right)\text{d}x}-2\int\limits_{0}^{1}{g\left( x \right)\text{d}x}=-8$
$\Leftrightarrow 2-2\int\limits_{0}^{1}{g\left( x \right)\text{d}x}=-8$ $\Leftrightarrow \int\limits_{0}^{1}{g\left( x \right)\text{d}x}=5$.
Đáp án B.