$$$\frac{\cos{\left(x \right)} \cot{\left(x \right)}}{\sin{\left(x \right)}}$$$ 的积分

求$$$\int \frac{\cos{\left(x \right)} \cot{\left(x \right)}}{\sin{\left(x \right)}}\, dx$$$。

化简被积函数:

$${\color{red}{\int{\frac{\cos{\left(x \right)} \cot{\left(x \right)}}{\sin{\left(x \right)}} d x}}} = {\color{red}{\int{\left(-1 + \frac{1}{\sin^{2}{\left(x \right)}}\right)d x}}}$$

逐项积分：

$${\color{red}{\int{\left(-1 + \frac{1}{\sin^{2}{\left(x \right)}}\right)d x}}} = {\color{red}{\left(- \int{1 d x} + \int{\frac{1}{\sin^{2}{\left(x \right)}} d x}\right)}}$$

应用常数法则 $$$\int c\, dx = c x$$$，使用 $$$c=1$$$：

$$\int{\frac{1}{\sin^{2}{\left(x \right)}} d x} - {\color{red}{\int{1 d x}}} = \int{\frac{1}{\sin^{2}{\left(x \right)}} d x} - {\color{red}{x}}$$

将被积函数用余割表示:

$$- x + {\color{red}{\int{\frac{1}{\sin^{2}{\left(x \right)}} d x}}} = - x + {\color{red}{\int{\csc^{2}{\left(x \right)} d x}}}$$

$$$\csc^{2}{\left(x \right)}$$$ 的积分为 $$$\int{\csc^{2}{\left(x \right)} d x} = - \cot{\left(x \right)}$$$:

$$- x + {\color{red}{\int{\csc^{2}{\left(x \right)} d x}}} = - x + {\color{red}{\left(- \cot{\left(x \right)}\right)}}$$

因此，

$$\int{\frac{\cos{\left(x \right)} \cot{\left(x \right)}}{\sin{\left(x \right)}} d x} = - x - \cot{\left(x \right)}$$

加上积分常数：

$$\int{\frac{\cos{\left(x \right)} \cot{\left(x \right)}}{\sin{\left(x \right)}} d x} = - x - \cot{\left(x \right)}+C$$

$$$\int \frac{\cos{\left(x \right)} \cot{\left(x \right)}}{\sin{\left(x \right)}}\, dx = \left(- x - \cot{\left(x \right)}\right) + C$$$A