问题
通过凑微分,如何计算 [$\textcolor{Orange}{\int f(\ln x) \frac{1}{x} \mathrm{d} x}$] ?选项
[A]. $\int$ $f(\ln x) \frac{1}{x}$ $\mathrm{d} x$ $=$ $\int$ $f(\ln x)$ $\mathrm{d} (\ln x)$ $+$ $C$[B]. $\int$ $f(\ln x) \frac{1}{x}$ $\mathrm{d} x$ $=$ $\int$ $f(\ln x)$ $\mathrm{d} (\ln x)$
[C]. $\int$ $f(\ln x) \frac{1}{x}$ $\mathrm{d} x$ $=$ $- \int$ $f(\ln x)$ $\mathrm{d} (\ln x)$
[D]. $\int$ $f(\ln x) \frac{1}{x}$ $\mathrm{d} x$ $=$ $\int$ $f(\ln x)$ $\mathrm{d} x$
$$\int \textcolor{Red}{f(\ln x)} \textcolor{Green}{\times} \textcolor{Red}{\frac{1}{x}} \mathrm{d} \textcolor{Yellow}{x} =$$ $$\int \textcolor{Red}{f(\ln x)} \mathrm{d} (\textcolor{Yellow}{\ln x})$$