Integral de $$$\cos{\left(x \right)} \csc^{2}{\left(x \right)}$$$

Encontre $$$\int \cos{\left(x \right)} \csc^{2}{\left(x \right)}\, dx$$$.

Reescreva o integrando:

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

Seja $$$u=\sin{\left(x \right)}$$$.

Então $$$du=\left(\sin{\left(x \right)}\right)^{\prime }dx = \cos{\left(x \right)} dx$$$ (veja os passos »), e obtemos $$$\cos{\left(x \right)} dx = du$$$.

A integral torna-se

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

Aplique a regra da potência $$$\int u^{n}\, du = \frac{u^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ com $$$n=-2$$$:

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

Recorde que $$$u=\sin{\left(x \right)}$$$:

$$- {\color{red}{u}}^{-1} = - {\color{red}{\sin{\left(x \right)}}}^{-1}$$

Portanto,

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

Adicione a constante de integração:

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

$$$\int \cos{\left(x \right)} \csc^{2}{\left(x \right)}\, dx = - \frac{1}{\sin{\left(x \right)}} + C$$$A