问题
[$\textcolor{Orange}{\int \frac{1}{\cos x} \mathrm{d} x}$] 的积分该怎么计算？选项
[A]. $\int$ $\frac{1}{\cos x}$ $\mathrm{d} x$ $=$ $\ln |\tan x – \sec x|$ $+$ $C$[B]. $\int$ $\frac{1}{\cos x}$ $\mathrm{d} x$ $=$ $\ln |\sec x – \tan x|$ $+$ $C$
[C]. $\int$ $\frac{1}{\cos x}$ $\mathrm{d} x$ $=$ $\ln |\sec x + \tan x|$
[D]. $\int$ $\frac{1}{\cos x}$ $\mathrm{d} x$ $=$ $\ln |\sec x + \tan x|$ $+$ $C$
$$\int \textcolor{Red}{\frac{1}{\cos x}} \mathrm{d} x =$$ $$\textcolor{Red}{\ln |\sec x + \tan x|} + \textcolor{Yelllow}{C}.$$