Integralen av $$$x^{6} \ln\left(x\right)$$$

Bestäm $$$\int x^{6} \ln\left(x\right)\, dx$$$.

För integralen $$$\int{x^{6} \ln{\left(x \right)} d x}$$$, använd partiell integration $$$\int \operatorname{u} \operatorname{dv} = \operatorname{u}\operatorname{v} - \int \operatorname{v} \operatorname{du}$$$.

Låt $$$\operatorname{u}=\ln{\left(x \right)}$$$ och $$$\operatorname{dv}=x^{6} dx$$$.

Då gäller $$$\operatorname{du}=\left(\ln{\left(x \right)}\right)^{\prime }dx=\frac{dx}{x}$$$ (stegen kan ses ») och $$$\operatorname{v}=\int{x^{6} d x}=\frac{x^{7}}{7}$$$ (stegen kan ses »).

Alltså,

$${\color{red}{\int{x^{6} \ln{\left(x \right)} d x}}}={\color{red}{\left(\ln{\left(x \right)} \cdot \frac{x^{7}}{7}-\int{\frac{x^{7}}{7} \cdot \frac{1}{x} d x}\right)}}={\color{red}{\left(\frac{x^{7} \ln{\left(x \right)}}{7} - \int{\frac{x^{6}}{7} d x}\right)}}$$

Tillämpa konstantfaktorregeln $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ med $$$c=\frac{1}{7}$$$ och $$$f{\left(x \right)} = x^{6}$$$:

$$\frac{x^{7} \ln{\left(x \right)}}{7} - {\color{red}{\int{\frac{x^{6}}{7} d x}}} = \frac{x^{7} \ln{\left(x \right)}}{7} - {\color{red}{\left(\frac{\int{x^{6} d x}}{7}\right)}}$$

Tillämpa potensregeln $$$\int x^{n}\, dx = \frac{x^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ med $$$n=6$$$:

$$\frac{x^{7} \ln{\left(x \right)}}{7} - \frac{{\color{red}{\int{x^{6} d x}}}}{7}=\frac{x^{7} \ln{\left(x \right)}}{7} - \frac{{\color{red}{\frac{x^{1 + 6}}{1 + 6}}}}{7}=\frac{x^{7} \ln{\left(x \right)}}{7} - \frac{{\color{red}{\left(\frac{x^{7}}{7}\right)}}}{7}$$

Alltså,

$$\int{x^{6} \ln{\left(x \right)} d x} = \frac{x^{7} \ln{\left(x \right)}}{7} - \frac{x^{7}}{49}$$

Förenkla:

$$\int{x^{6} \ln{\left(x \right)} d x} = \frac{x^{7} \left(7 \ln{\left(x \right)} - 1\right)}{49}$$

Lägg till integrationskonstanten:

$$\int{x^{6} \ln{\left(x \right)} d x} = \frac{x^{7} \left(7 \ln{\left(x \right)} - 1\right)}{49}+C$$

$$$\int x^{6} \ln\left(x\right)\, dx = \frac{x^{7} \left(7 \ln\left(x\right) - 1\right)}{49} + C$$$A