Integraal van $$$\operatorname{atan}{\left(\sqrt{x} \right)}$$$

Bepaal $$$\int \operatorname{atan}{\left(\sqrt{x} \right)}\, dx$$$.

Voor de integraal $$$\int{\operatorname{atan}{\left(\sqrt{x} \right)} d x}$$$, gebruik partiële integratie $$$\int \operatorname{u} \operatorname{dv} = \operatorname{u}\operatorname{v} - \int \operatorname{v} \operatorname{du}$$$.

Zij $$$\operatorname{u}=\operatorname{atan}{\left(\sqrt{x} \right)}$$$ en $$$\operatorname{dv}=dx$$$.

Dan $$$\operatorname{du}=\left(\operatorname{atan}{\left(\sqrt{x} \right)}\right)^{\prime }dx=\frac{1}{2 \sqrt{x} \left(x + 1\right)} dx$$$ (de stappen zijn te zien ») en $$$\operatorname{v}=\int{1 d x}=x$$$ (de stappen zijn te zien »).

Dus,

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

Vereenvoudig de integraand:

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

Pas de constante-veelvoudregel $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ toe met $$$c=\frac{1}{2}$$$ en $$$f{\left(x \right)} = \frac{\sqrt{x}}{x + 1}$$$:

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

Zij $$$u=\sqrt{x}$$$.

Dan $$$du=\left(\sqrt{x}\right)^{\prime }dx = \frac{1}{2 \sqrt{x}} dx$$$ (de stappen zijn te zien »), en dan geldt dat $$$\frac{dx}{\sqrt{x}} = 2 du$$$.

Dus,

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

Pas de constante-veelvoudregel $$$\int c f{\left(u \right)}\, du = c \int f{\left(u \right)}\, du$$$ toe met $$$c=2$$$ en $$$f{\left(u \right)} = \frac{u^{2}}{u^{2} + 1}$$$:

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

Herschrijf en splits de breuk:

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

Integreer termgewijs:

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

Pas de constantenregel $$$\int c\, du = c u$$$ toe met $$$c=1$$$:

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

De integraal van $$$\frac{1}{u^{2} + 1}$$$ is $$$\int{\frac{1}{u^{2} + 1} d u} = \operatorname{atan}{\left(u \right)}$$$:

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

We herinneren eraan dat $$$u=\sqrt{x}$$$:

$$x \operatorname{atan}{\left(\sqrt{x} \right)} + \operatorname{atan}{\left({\color{red}{u}} \right)} - {\color{red}{u}} = x \operatorname{atan}{\left(\sqrt{x} \right)} + \operatorname{atan}{\left({\color{red}{\sqrt{x}}} \right)} - {\color{red}{\sqrt{x}}}$$

Dus,

$$\int{\operatorname{atan}{\left(\sqrt{x} \right)} d x} = - \sqrt{x} + x \operatorname{atan}{\left(\sqrt{x} \right)} + \operatorname{atan}{\left(\sqrt{x} \right)}$$

Voeg de integratieconstante toe:

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

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