问题
[$\textcolor{Orange}{\int \frac{1}{\sqrt{x^{2} \pm a^{2}}} \mathrm{d} x}$] 的积分该怎么计算?选项
[A]. $\int$ $\frac{1}{\sqrt{x^{2} \pm a^{2}}}$ $\mathrm{d} x$ $=$ $\ln \Big| x + \sqrt{x^{2} \pm a^{2}} \Big|$ $+$ $C$[B]. $\int$ $\frac{1}{\sqrt{x^{2} \pm a^{2}}}$ $\mathrm{d} x$ $=$ $\ln \Big| x \pm \sqrt{x^{2} \pm a^{2}} \Big|$ $+$ $C$
[C]. $\int$ $\frac{1}{\sqrt{x^{2} \pm a^{2}}}$ $\mathrm{d} x$ $=$ $\ln \Big| x + \sqrt{x^{2} \mp a^{2}} \Big|$ $+$ $C$
[D]. $\int$ $\frac{1}{\sqrt{x^{2} \pm a^{2}}}$ $\mathrm{d} x$ $=$ $\ln \Big| x + \sqrt{x^{2} \pm a^{2}} \Big|$