问题
[$\textcolor{Orange}{\int (\sec x \times \tan x) \mathrm{d} x}$] 的积分该怎么计算？选项
[A]. $\int$ $(\sec x \tan x)$ $\mathrm{d} x$ $=$ $\csc x$ $+$ $C$[B]. $\int$ $(\sec x \tan x)$ $\mathrm{d} x$ $=$ $- \sec x$ $+$ $C$
[C]. $\int$ $(\sec x \tan x)$ $\mathrm{d} x$ $=$ $\sec x$
[D]. $\int$ $(\sec x \tan x)$ $\mathrm{d} x$ $=$ $\sec x$ $+$ $C$
$$\int \textcolor{Red}{(\sec x \times \tan x)} \mathrm{d} x =$$ $$\int \textcolor{Red}{(\frac{1}{\cos x} \times \frac{\sin x}{\cos x})} \mathrm{d} x =$$ $$\textcolor{Red}{\sec x} + \textcolor{Yellow}{C} =$$ $$\textcolor{Red}{\frac{1}{\cos x}} + \textcolor{Yellow}{C}.$$