Cho hàm số $f(x)$ liên tục trên $\mathbb{R}$ thỏa mãn...

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Khi đó
$$ $\left( 2 \right)\left( 1 \right)\left( 2 \right)\int\limits_{\dfrac{1}{2}}^{4}{\dfrac{f(x)}{x}\text{d}}x=\dfrac{5}{2}k=\int\limits_{\dfrac{1}{8}}^{1}{\dfrac{f(4x)}{x}\text{d}x}=\int\limits_{\dfrac{1}{8}}^{1}{\dfrac{f(4x)}{4x}\text{d}\left( 4x \right)}t=4x\left\{ \begin{aligned}
& x=1\Rightarrow t=4 \\
& x=\dfrac{1}{8}\Rightarrow t=\dfrac{1}{2} \\
\end{aligned} \right.k=\int\limits_{\dfrac{1}{2}}^{4}{\dfrac{f(t)}{t}\text{d}t}=\int\limits_{\dfrac{1}{2}}^{4}{\dfrac{f(x)}{x}\text{d}x}=\dfrac{3}{2}$