问题
[$\textcolor{Orange}{\int \frac{x}{1 + x^{2}} \mathrm{d} x}$] 的积分该怎么计算?选项
[A]. $\int$ $\frac{x}{1 + x^{2}}$ $\mathrm{d} x$ $=$ $\frac{1}{2}$ $\ln (x + x^{2})$ $+$ $C$[B]. $\int$ $\frac{x}{1 + x^{2}}$ $\mathrm{d} x$ $=$ $\frac{1}{2}$ $\ln (1 + x^{2})$
[C]. $\int$ $\frac{x}{1 + x^{2}}$ $\mathrm{d} x$ $=$ $\frac{1}{2}$ $\ln (1 + x^{2})$ $+$ $C$
[D]. $\int$ $\frac{x}{1 + x^{2}}$ $\mathrm{d} x$ $=$ $\frac{1}{2}$ $\ln (1 + x)$ $+$ $C$
$$\int \textcolor{Red}{\frac{x}{1 + x^{2}}} \mathrm{d} x=$$ $$\textcolor{Red}{\frac{1}{2}} \textcolor{Green}{\times} \textcolor{Red}{\ln (1 + x^{2})} + \textcolor{Yellow}{C}.$$