Tìm nguyên hàm: \(I = \smallint \left( {\frac{1}{{{{\ln }^2}x}} – \frac{1}{{\ln x}}} \right)dx\)

\(\begin{array}{l}
\frac{1}{{{{\ln }^2}x}} – \frac{1}{{\ln x}} = \frac{{1 – \ln x}}{{{{\ln }^2}x}} = \frac{{x\left( {\ln x} \right)’ – \left( x \right)’\ln x}}{{{{\ln }^2}x}} = \left( {\frac{x}{{\ln x}}} \right)’\\
 \Rightarrow I = \int {\left( {\frac{x}{{\ln x}}} \right)’dx = \frac{x}{{\ln x}} + C} 
\end{array}\)