$$$- 6 \operatorname{asin}{\left(5 x \right)}$$$ 的积分

求$$$\int \left(- 6 \operatorname{asin}{\left(5 x \right)}\right)\, dx$$$。

对 $$$c=-6$$$ 和 $$$f{\left(x \right)} = \operatorname{asin}{\left(5 x \right)}$$$ 应用常数倍法则 $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$：

$${\color{red}{\int{\left(- 6 \operatorname{asin}{\left(5 x \right)}\right)d x}}} = {\color{red}{\left(- 6 \int{\operatorname{asin}{\left(5 x \right)} d x}\right)}}$$

设$$$u=5 x$$$。

则$$$du=\left(5 x\right)^{\prime }dx = 5 dx$$$ (步骤见»)，并有$$$dx = \frac{du}{5}$$$。

该积分可以改写为

$$- 6 {\color{red}{\int{\operatorname{asin}{\left(5 x \right)} d x}}} = - 6 {\color{red}{\int{\frac{\operatorname{asin}{\left(u \right)}}{5} d u}}}$$

对 $$$c=\frac{1}{5}$$$ 和 $$$f{\left(u \right)} = \operatorname{asin}{\left(u \right)}$$$ 应用常数倍法则 $$$\int c f{\left(u \right)}\, du = c \int f{\left(u \right)}\, du$$$：

$$- 6 {\color{red}{\int{\frac{\operatorname{asin}{\left(u \right)}}{5} d u}}} = - 6 {\color{red}{\left(\frac{\int{\operatorname{asin}{\left(u \right)} d u}}{5}\right)}}$$

对于积分$$$\int{\operatorname{asin}{\left(u \right)} d u}$$$，使用分部积分法$$$\int \operatorname{\omega} \operatorname{dv} = \operatorname{\omega}\operatorname{v} - \int \operatorname{v} \operatorname{d\omega}$$$。

设 $$$\operatorname{\omega}=\operatorname{asin}{\left(u \right)}$$$ 和 $$$\operatorname{dv}=du$$$。

则 $$$\operatorname{d\omega}=\left(\operatorname{asin}{\left(u \right)}\right)^{\prime }du=\frac{du}{\sqrt{1 - u^{2}}}$$$ (步骤见 »)，并且 $$$\operatorname{v}=\int{1 d u}=u$$$ (步骤见 »)。

积分变为

$$- \frac{6 {\color{red}{\int{\operatorname{asin}{\left(u \right)} d u}}}}{5}=- \frac{6 {\color{red}{\left(\operatorname{asin}{\left(u \right)} \cdot u-\int{u \cdot \frac{1}{\sqrt{1 - u^{2}}} d u}\right)}}}{5}=- \frac{6 {\color{red}{\left(u \operatorname{asin}{\left(u \right)} - \int{\frac{u}{\sqrt{1 - u^{2}}} d u}\right)}}}{5}$$

设$$$v=1 - u^{2}$$$。

则$$$dv=\left(1 - u^{2}\right)^{\prime }du = - 2 u du$$$ (步骤见»)，并有$$$u du = - \frac{dv}{2}$$$。

因此，

$$- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} + \frac{6 {\color{red}{\int{\frac{u}{\sqrt{1 - u^{2}}} d u}}}}{5} = - \frac{6 u \operatorname{asin}{\left(u \right)}}{5} + \frac{6 {\color{red}{\int{\left(- \frac{1}{2 \sqrt{v}}\right)d v}}}}{5}$$

对 $$$c=- \frac{1}{2}$$$ 和 $$$f{\left(v \right)} = \frac{1}{\sqrt{v}}$$$ 应用常数倍法则 $$$\int c f{\left(v \right)}\, dv = c \int f{\left(v \right)}\, dv$$$：

$$- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} + \frac{6 {\color{red}{\int{\left(- \frac{1}{2 \sqrt{v}}\right)d v}}}}{5} = - \frac{6 u \operatorname{asin}{\left(u \right)}}{5} + \frac{6 {\color{red}{\left(- \frac{\int{\frac{1}{\sqrt{v}} d v}}{2}\right)}}}{5}$$

应用幂法则 $$$\int v^{n}\, dv = \frac{v^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$，其中 $$$n=- \frac{1}{2}$$$：

$$- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} - \frac{3 {\color{red}{\int{\frac{1}{\sqrt{v}} d v}}}}{5}=- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} - \frac{3 {\color{red}{\int{v^{- \frac{1}{2}} d v}}}}{5}=- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} - \frac{3 {\color{red}{\frac{v^{- \frac{1}{2} + 1}}{- \frac{1}{2} + 1}}}}{5}=- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} - \frac{3 {\color{red}{\left(2 v^{\frac{1}{2}}\right)}}}{5}=- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} - \frac{3 {\color{red}{\left(2 \sqrt{v}\right)}}}{5}$$

回忆一下 $$$v=1 - u^{2}$$$:

$$- \frac{6 u \operatorname{asin}{\left(u \right)}}{5} - \frac{6 \sqrt{{\color{red}{v}}}}{5} = - \frac{6 u \operatorname{asin}{\left(u \right)}}{5} - \frac{6 \sqrt{{\color{red}{\left(1 - u^{2}\right)}}}}{5}$$

回忆一下 $$$u=5 x$$$:

$$- \frac{6 \sqrt{1 - {\color{red}{u}}^{2}}}{5} - \frac{6 {\color{red}{u}} \operatorname{asin}{\left({\color{red}{u}} \right)}}{5} = - \frac{6 \sqrt{1 - {\color{red}{\left(5 x\right)}}^{2}}}{5} - \frac{6 {\color{red}{\left(5 x\right)}} \operatorname{asin}{\left({\color{red}{\left(5 x\right)}} \right)}}{5}$$

因此，

$$\int{\left(- 6 \operatorname{asin}{\left(5 x \right)}\right)d x} = - 6 x \operatorname{asin}{\left(5 x \right)} - \frac{6 \sqrt{1 - 25 x^{2}}}{5}$$

加上积分常数：

$$\int{\left(- 6 \operatorname{asin}{\left(5 x \right)}\right)d x} = - 6 x \operatorname{asin}{\left(5 x \right)} - \frac{6 \sqrt{1 - 25 x^{2}}}{5}+C$$

$$$\int \left(- 6 \operatorname{asin}{\left(5 x \right)}\right)\, dx = \left(- 6 x \operatorname{asin}{\left(5 x \right)} - \frac{6 \sqrt{1 - 25 x^{2}}}{5}\right) + C$$$A