Integraal van $$$\frac{\ln\left(u\right)}{u}$$$

Bepaal $$$\int \frac{\ln\left(u\right)}{u}\, du$$$.

Zij $$$v=\ln{\left(u \right)}$$$.

Dan $$$dv=\left(\ln{\left(u \right)}\right)^{\prime }du = \frac{du}{u}$$$ (de stappen zijn te zien »), en dan geldt dat $$$\frac{du}{u} = dv$$$.

Dus,

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

Pas de machtsregel $$$\int v^{n}\, dv = \frac{v^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ toe met $$$n=1$$$:

$${\color{red}{\int{v d v}}}={\color{red}{\frac{v^{1 + 1}}{1 + 1}}}={\color{red}{\left(\frac{v^{2}}{2}\right)}}$$

We herinneren eraan dat $$$v=\ln{\left(u \right)}$$$:

$$\frac{{\color{red}{v}}^{2}}{2} = \frac{{\color{red}{\ln{\left(u \right)}}}^{2}}{2}$$

Dus,

$$\int{\frac{\ln{\left(u \right)}}{u} d u} = \frac{\ln{\left(u \right)}^{2}}{2}$$

Voeg de integratieconstante toe:

$$\int{\frac{\ln{\left(u \right)}}{u} d u} = \frac{\ln{\left(u \right)}^{2}}{2}+C$$

$$$\int \frac{\ln\left(u\right)}{u}\, du = \frac{\ln^{2}\left(u\right)}{2} + C$$$A