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Câu hỏi: Cho $\int\limits_{2}^{5}{f\left( x \right) \text{d}x=12}$. Khi đó $\int\limits_{5}^{2}{\left[ 1-6f\left( x \right) \right] \text{d}x}$ bằng
A. $79$.
B. $69$.
C. $72$.
D. $74$
A. $79$.
B. $69$.
C. $72$.
D. $74$
Ta có: $\int\limits_{5}^{2}{\left[ 1-6f\left( x \right) \right] \text{d}x}$ $=\int\limits_{2}^{5}{\left[ 6f\left( x \right)-1 \right] \text{d}x}$ $=6\int\limits_{2}^{5}{f\left( x \right) \text{d}x-}\int\limits_{2}^{5}{ \text{d}x}$ $=6.12-5+2$ $=69$.
Đáp án B.