Biết $\int\limits_{e}^{{{e}^{4}}}{f\left( \ln x...

Đặt . \)">t=\ln x\Rightarrow dt=\dfrac{1}{x}dx\Rightarrow 4=\int\limits_{e}^{{{e}^{4}}}{f\left( \ln x \right)\dfrac{1}{x}dx}=\int\limits_{1}^{4}{f\left( t \right)dt}\Rightarrow I=\int\limits_{1}^{4}{f\left( x \right)dx}=4$.