Integral de $$$\ln\left(9 x - 8\right)$$$

Encontre $$$\int \ln\left(9 x - 8\right)\, dx$$$.

Seja $$$u=9 x - 8$$$.

Então $$$du=\left(9 x - 8\right)^{\prime }dx = 9 dx$$$ (veja os passos »), e obtemos $$$dx = \frac{du}{9}$$$.

A integral torna-se

$${\color{red}{\int{\ln{\left(9 x - 8 \right)} d x}}} = {\color{red}{\int{\frac{\ln{\left(u \right)}}{9} d u}}}$$

Aplique a regra do múltiplo constante $$$\int c f{\left(u \right)}\, du = c \int f{\left(u \right)}\, du$$$ usando $$$c=\frac{1}{9}$$$ e $$$f{\left(u \right)} = \ln{\left(u \right)}$$$:

$${\color{red}{\int{\frac{\ln{\left(u \right)}}{9} d u}}} = {\color{red}{\left(\frac{\int{\ln{\left(u \right)} d u}}{9}\right)}}$$

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

Sejam $$$\operatorname{t}=\ln{\left(u \right)}$$$ e $$$\operatorname{dv}=du$$$.

Então $$$\operatorname{dt}=\left(\ln{\left(u \right)}\right)^{\prime }du=\frac{du}{u}$$$ (os passos podem ser vistos ») e $$$\operatorname{v}=\int{1 d u}=u$$$ (os passos podem ser vistos »).

Logo,

$$\frac{{\color{red}{\int{\ln{\left(u \right)} d u}}}}{9}=\frac{{\color{red}{\left(\ln{\left(u \right)} \cdot u-\int{u \cdot \frac{1}{u} d u}\right)}}}{9}=\frac{{\color{red}{\left(u \ln{\left(u \right)} - \int{1 d u}\right)}}}{9}$$

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

$$\frac{u \ln{\left(u \right)}}{9} - \frac{{\color{red}{\int{1 d u}}}}{9} = \frac{u \ln{\left(u \right)}}{9} - \frac{{\color{red}{u}}}{9}$$

Recorde que $$$u=9 x - 8$$$:

$$- \frac{{\color{red}{u}}}{9} + \frac{{\color{red}{u}} \ln{\left({\color{red}{u}} \right)}}{9} = - \frac{{\color{red}{\left(9 x - 8\right)}}}{9} + \frac{{\color{red}{\left(9 x - 8\right)}} \ln{\left({\color{red}{\left(9 x - 8\right)}} \right)}}{9}$$

Portanto,

$$\int{\ln{\left(9 x - 8 \right)} d x} = - x + \frac{\left(9 x - 8\right) \ln{\left(9 x - 8 \right)}}{9} + \frac{8}{9}$$

Simplifique:

$$\int{\ln{\left(9 x - 8 \right)} d x} = \frac{\left(9 x - 8\right) \left(\ln{\left(9 x - 8 \right)} - 1\right)}{9}$$

Adicione a constante de integração:

$$\int{\ln{\left(9 x - 8 \right)} d x} = \frac{\left(9 x - 8\right) \left(\ln{\left(9 x - 8 \right)} - 1\right)}{9}+C$$

$$$\int \ln\left(9 x - 8\right)\, dx = \frac{\left(9 x - 8\right) \left(\ln\left(9 x - 8\right) - 1\right)}{9} + C$$$A