$$$\frac{\sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{3}}$$$ 對 $$$\pi$$$ 的積分

求$$$\int \frac{\sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{3}}\, d\pi$$$。

套用常數倍法則 $$$\int c f{\left(\pi \right)}\, d\pi = c \int f{\left(\pi \right)}\, d\pi$$$，使用 $$$c=\sin^{2}{\left(z \right)}$$$ 與 $$$f{\left(\pi \right)} = \frac{1}{\left(- \frac{\pi}{6} + z\right)^{3}}$$$：

$${\color{red}{\int{\frac{\sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{3}} d \pi}}} = {\color{red}{\sin^{2}{\left(z \right)} \int{\frac{1}{\left(- \frac{\pi}{6} + z\right)^{3}} d \pi}}}$$

令 $$$u=- \frac{\pi}{6} + z$$$。

則 $$$du=\left(- \frac{\pi}{6} + z\right)^{\prime }d\pi = - \frac{d\pi}{6}$$$ (步驟見»)，並可得 $$$d\pi = - 6 du$$$。

該積分可改寫為

$$\sin^{2}{\left(z \right)} {\color{red}{\int{\frac{1}{\left(- \frac{\pi}{6} + z\right)^{3}} d \pi}}} = \sin^{2}{\left(z \right)} {\color{red}{\int{\left(- \frac{6}{u^{3}}\right)d u}}}$$

套用常數倍法則 $$$\int c f{\left(u \right)}\, du = c \int f{\left(u \right)}\, du$$$，使用 $$$c=-6$$$ 與 $$$f{\left(u \right)} = \frac{1}{u^{3}}$$$：

$$\sin^{2}{\left(z \right)} {\color{red}{\int{\left(- \frac{6}{u^{3}}\right)d u}}} = \sin^{2}{\left(z \right)} {\color{red}{\left(- 6 \int{\frac{1}{u^{3}} d u}\right)}}$$

套用冪次法則 $$$\int u^{n}\, du = \frac{u^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$，以 $$$n=-3$$$：

$$- 6 \sin^{2}{\left(z \right)} {\color{red}{\int{\frac{1}{u^{3}} d u}}}=- 6 \sin^{2}{\left(z \right)} {\color{red}{\int{u^{-3} d u}}}=- 6 \sin^{2}{\left(z \right)} {\color{red}{\frac{u^{-3 + 1}}{-3 + 1}}}=- 6 \sin^{2}{\left(z \right)} {\color{red}{\left(- \frac{u^{-2}}{2}\right)}}=- 6 \sin^{2}{\left(z \right)} {\color{red}{\left(- \frac{1}{2 u^{2}}\right)}}$$

回顧一下 $$$u=- \frac{\pi}{6} + z$$$：

$$3 \sin^{2}{\left(z \right)} {\color{red}{u}}^{-2} = 3 \sin^{2}{\left(z \right)} {\color{red}{\left(- \frac{\pi}{6} + z\right)}}^{-2}$$

因此，

$$\int{\frac{\sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{3}} d \pi} = \frac{3 \sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{2}}$$

化簡：

$$\int{\frac{\sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{3}} d \pi} = \frac{108 \sin^{2}{\left(z \right)}}{\left(- \pi + 6 z\right)^{2}}$$

加上積分常數：

$$\int{\frac{\sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{3}} d \pi} = \frac{108 \sin^{2}{\left(z \right)}}{\left(- \pi + 6 z\right)^{2}}+C$$

$$$\int \frac{\sin^{2}{\left(z \right)}}{\left(- \frac{\pi}{6} + z\right)^{3}}\, d\pi = \frac{108 \sin^{2}{\left(z \right)}}{\left(- \pi + 6 z\right)^{2}} + C$$$A