$$$- 8 x + \tan{\left(x \right)} \sec{\left(x \right)}$$$ 的積分

求$$$\int \left(- 8 x + \tan{\left(x \right)} \sec{\left(x \right)}\right)\, dx$$$。

逐項積分：

$${\color{red}{\int{\left(- 8 x + \tan{\left(x \right)} \sec{\left(x \right)}\right)d x}}} = {\color{red}{\left(- \int{8 x d x} + \int{\tan{\left(x \right)} \sec{\left(x \right)} d x}\right)}}$$

套用常數倍法則 $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$，使用 $$$c=8$$$ 與 $$$f{\left(x \right)} = x$$$：

$$\int{\tan{\left(x \right)} \sec{\left(x \right)} d x} - {\color{red}{\int{8 x d x}}} = \int{\tan{\left(x \right)} \sec{\left(x \right)} d x} - {\color{red}{\left(8 \int{x d x}\right)}}$$

套用冪次法則 $$$\int x^{n}\, dx = \frac{x^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$，以 $$$n=1$$$：

$$\int{\tan{\left(x \right)} \sec{\left(x \right)} d x} - 8 {\color{red}{\int{x d x}}}=\int{\tan{\left(x \right)} \sec{\left(x \right)} d x} - 8 {\color{red}{\frac{x^{1 + 1}}{1 + 1}}}=\int{\tan{\left(x \right)} \sec{\left(x \right)} d x} - 8 {\color{red}{\left(\frac{x^{2}}{2}\right)}}$$

$$$\tan{\left(x \right)} \sec{\left(x \right)}$$$ 的積分是 $$$\int{\tan{\left(x \right)} \sec{\left(x \right)} d x} = \sec{\left(x \right)}$$$：

$$- 4 x^{2} + {\color{red}{\int{\tan{\left(x \right)} \sec{\left(x \right)} d x}}} = - 4 x^{2} + {\color{red}{\sec{\left(x \right)}}}$$

因此，

$$\int{\left(- 8 x + \tan{\left(x \right)} \sec{\left(x \right)}\right)d x} = - 4 x^{2} + \sec{\left(x \right)}$$

加上積分常數：

$$\int{\left(- 8 x + \tan{\left(x \right)} \sec{\left(x \right)}\right)d x} = - 4 x^{2} + \sec{\left(x \right)}+C$$

$$$\int \left(- 8 x + \tan{\left(x \right)} \sec{\left(x \right)}\right)\, dx = \left(- 4 x^{2} + \sec{\left(x \right)}\right) + C$$$A