Integral de $$$\operatorname{asec}{\left(x \right)}$$$

Encontre $$$\int \operatorname{asec}{\left(x \right)}\, dx$$$.

Para a integral $$$\int{\operatorname{asec}{\left(x \right)} d x}$$$, use integração por partes $$$\int \operatorname{u} \operatorname{dv} = \operatorname{u}\operatorname{v} - \int \operatorname{v} \operatorname{du}$$$.

Sejam $$$\operatorname{u}=\operatorname{asec}{\left(x \right)}$$$ e $$$\operatorname{dv}=dx$$$.

Então $$$\operatorname{du}=\left(\operatorname{asec}{\left(x \right)}\right)^{\prime }dx=\frac{\left|{x}\right|}{x^{2} \sqrt{x^{2} - 1}} dx$$$ (os passos podem ser vistos ») e $$$\operatorname{v}=\int{1 d x}=x$$$ (os passos podem ser vistos »).

A integral pode ser reescrita como

$${\color{red}{\int{\operatorname{asec}{\left(x \right)} d x}}}={\color{red}{\left(\operatorname{asec}{\left(x \right)} \cdot x-\int{x \cdot \frac{\left|{x}\right|}{x^{2} \sqrt{x^{2} - 1}} d x}\right)}}={\color{red}{\left(x \operatorname{asec}{\left(x \right)} - \int{\frac{\left|{x}\right|}{x \sqrt{x^{2} - 1}} d x}\right)}}$$

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

Então $$$dx=\left(\cosh{\left(u \right)}\right)^{\prime }du = \sinh{\left(u \right)} du$$$ (os passos podem ser vistos »).

Além disso, segue-se que $$$u=\operatorname{acosh}{\left(x \right)}$$$.

O integrando torna-se

$$$\frac{\left|{x}\right|}{x \sqrt{x^{2} - 1}} = \frac{1}{\sqrt{\cosh^{2}{\left( u \right)} - 1}}$$$

Use a identidade $$$\cosh^{2}{\left( u \right)} - 1 = \sinh^{2}{\left( u \right)}$$$:

$$$\frac{1}{\sqrt{\cosh^{2}{\left( u \right)} - 1}}=\frac{1}{\sqrt{\sinh^{2}{\left( u \right)}}}$$$

Supondo que $$$\sinh{\left( u \right)} \ge 0$$$, obtemos o seguinte:

$$$\frac{1}{\sqrt{\sinh^{2}{\left( u \right)}}} = \frac{1}{\sinh{\left( u \right)}}$$$

Logo,

$$x \operatorname{asec}{\left(x \right)} - {\color{red}{\int{\frac{\left|{x}\right|}{x \sqrt{x^{2} - 1}} d x}}} = x \operatorname{asec}{\left(x \right)} - {\color{red}{\int{1 d u}}}$$

Aplique a regra da constante $$$\int c\, du = c u$$$ usando $$$c=1$$$:

$$x \operatorname{asec}{\left(x \right)} - {\color{red}{\int{1 d u}}} = x \operatorname{asec}{\left(x \right)} - {\color{red}{u}}$$

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

$$x \operatorname{asec}{\left(x \right)} - {\color{red}{u}} = x \operatorname{asec}{\left(x \right)} - {\color{red}{\operatorname{acosh}{\left(x \right)}}}$$

Portanto,

$$\int{\operatorname{asec}{\left(x \right)} d x} = x \operatorname{asec}{\left(x \right)} - \operatorname{acosh}{\left(x \right)}$$

Adicione a constante de integração:

$$\int{\operatorname{asec}{\left(x \right)} d x} = x \operatorname{asec}{\left(x \right)} - \operatorname{acosh}{\left(x \right)}+C$$

$$$\int \operatorname{asec}{\left(x \right)}\, dx = \left(x \operatorname{asec}{\left(x \right)} - \operatorname{acosh}{\left(x \right)}\right) + C$$$A