Integral de $$$\sqrt{- x y + y}$$$ em relação a $$$y$$$

Encontre $$$\int \sqrt{- x y + y}\, dy$$$.

Seja $$$u=- x y + y$$$.

Então $$$du=\left(- x y + y\right)^{\prime }dy = \left(1 - x\right) dy$$$ (veja os passos »), e obtemos $$$dy = \frac{du}{1 - x}$$$.

A integral pode ser reescrita como

$${\color{red}{\int{\sqrt{- x y + y} d y}}} = {\color{red}{\int{\frac{\sqrt{u}}{1 - x} d u}}}$$

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

$${\color{red}{\int{\frac{\sqrt{u}}{1 - x} d u}}} = {\color{red}{\frac{\int{\sqrt{u} d u}}{1 - x}}}$$

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

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

Recorde que $$$u=- x y + y$$$:

$$\frac{2 {\color{red}{u}}^{\frac{3}{2}}}{3 \left(1 - x\right)} = \frac{2 {\color{red}{\left(- x y + y\right)}}^{\frac{3}{2}}}{3 \left(1 - x\right)}$$

Portanto,

$$\int{\sqrt{- x y + y} d y} = \frac{2 \left(- x y + y\right)^{\frac{3}{2}}}{3 \left(1 - x\right)}$$

Simplifique:

$$\int{\sqrt{- x y + y} d y} = \frac{2 y \sqrt{y \left(1 - x\right)}}{3}$$

Adicione a constante de integração:

$$\int{\sqrt{- x y + y} d y} = \frac{2 y \sqrt{y \left(1 - x\right)}}{3}+C$$

$$$\int \sqrt{- x y + y}\, dy = \frac{2 y \sqrt{y \left(1 - x\right)}}{3} + C$$$A