Câu hỏi: Cho liên tục trên và thỏa mãn . Tích phân bằng
A. .$$
B. $28C. \)"> 36D. \)"> 16
A.
B. $28
Ta có: \)">\int\limits_{0}^{1}{f\left( 2x \right)\text{d}x=2}\Leftrightarrow \frac{1}{2}\int\limits_{0}^{1}{f\left( 2x \right)\text{d}\left( 2x \right)=2}\Leftrightarrow \int\limits_{0}^{2}{f\left( x \right)\text{d}x=4} \left\{ \begin{aligned}
& u=x \\
& \text{d}v={f}'\left( x \right)\text{dx} \\
\end{aligned} \right.\Rightarrow \left\{ \begin{aligned}
& \text{d}u=\text{d}x \\
& v=f\left( x \right) \\
\end{aligned} \right. \Rightarrow \int\limits_{0}^{2}{x{f}'\left( x \right)}\text{d}x=\left. xf\left( x \right) \right|_{0}^{2}-\int\limits_{0}^{2}{f\left( x \right)}\text{d}x=2f\left( 2 \right)-4=32-4=28$.
& u=x \\
& \text{d}v={f}'\left( x \right)\text{dx} \\
\end{aligned} \right.\Rightarrow \left\{ \begin{aligned}
& \text{d}u=\text{d}x \\
& v=f\left( x \right) \\
\end{aligned} \right.
Đáp án B.