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