问题
通过凑微分,如何计算 [$\textcolor{Orange}{\int f(\sqrt{x}) \frac{1}{\sqrt{x}} \mathrm{d} x}$] ?选项
[A]. $\int$ $f(\sqrt{x}) \frac{1}{\sqrt{x}}$ $\mathrm{d} x$ $=$ $2 \int$ $f(\sqrt{x})$ $\mathrm{d} x$[B]. $\int$ $f(\sqrt{x}) \frac{1}{\sqrt{x}}$ $\mathrm{d} x$ $=$ $-2$ $\int$ $f(\sqrt{x})$ $\mathrm{d} (\sqrt{x})$
[C]. $\int$ $f(\sqrt{x}) \frac{1}{\sqrt{x}}$ $\mathrm{d} x$ $=$ $2 \int$ $f(\sqrt{x})$ $\mathrm{d} (\sqrt{x})$
[D]. $\int$ $f(\sqrt{x}) \frac{1}{\sqrt{x}}$ $\mathrm{d} x$ $=$ $\int$ $f(\sqrt{x})$ $\mathrm{d} (\sqrt{x})$
$$\int \textcolor{Red}{f(\sqrt{x})} \textcolor{Green}{\times} \textcolor{Red}{\frac{1}{\sqrt{x}}} \mathrm{d} \textcolor{Yellow}{x} =$$ $$\textcolor{Orange}{2} \int \textcolor{Red}{f(\sqrt{x})} \mathrm{d} (\textcolor{Yellow}{\sqrt{x}}).$$