Funktion $$$\frac{2}{5 - x^{2}}$$$ integraali

Määritä $$$\int \frac{2}{5 - x^{2}}\, dx$$$.

Sovella vakiokertoimen sääntöä $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ käyttäen $$$c=2$$$ ja $$$f{\left(x \right)} = \frac{1}{5 - x^{2}}$$$:

$${\color{red}{\int{\frac{2}{5 - x^{2}} d x}}} = {\color{red}{\left(2 \int{\frac{1}{5 - x^{2}} d x}\right)}}$$

Suorita osamurtokehittely (vaiheet voidaan nähdä kohdassa »):

$$2 {\color{red}{\int{\frac{1}{5 - x^{2}} d x}}} = 2 {\color{red}{\int{\left(\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} - \frac{\sqrt{5}}{10 \left(x - \sqrt{5}\right)}\right)d x}}}$$

Integroi termi kerrallaan:

$$2 {\color{red}{\int{\left(\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} - \frac{\sqrt{5}}{10 \left(x - \sqrt{5}\right)}\right)d x}}} = 2 {\color{red}{\left(- \int{\frac{\sqrt{5}}{10 \left(x - \sqrt{5}\right)} d x} + \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x}\right)}}$$

Sovella vakiokertoimen sääntöä $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ käyttäen $$$c=\frac{\sqrt{5}}{10}$$$ ja $$$f{\left(x \right)} = \frac{1}{x - \sqrt{5}}$$$:

$$2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x} - 2 {\color{red}{\int{\frac{\sqrt{5}}{10 \left(x - \sqrt{5}\right)} d x}}} = 2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x} - 2 {\color{red}{\left(\frac{\sqrt{5} \int{\frac{1}{x - \sqrt{5}} d x}}{10}\right)}}$$

Olkoon $$$u=x - \sqrt{5}$$$.

Tällöin $$$du=\left(x - \sqrt{5}\right)^{\prime }dx = 1 dx$$$ (vaiheet ovat nähtävissä ») ja saamme, että $$$dx = du$$$.

Siis,

$$2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x} - \frac{\sqrt{5} {\color{red}{\int{\frac{1}{x - \sqrt{5}} d x}}}}{5} = 2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x} - \frac{\sqrt{5} {\color{red}{\int{\frac{1}{u} d u}}}}{5}$$

Funktion $$$\frac{1}{u}$$$ integraali on $$$\int{\frac{1}{u} d u} = \ln{\left(\left|{u}\right| \right)}$$$:

$$2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x} - \frac{\sqrt{5} {\color{red}{\int{\frac{1}{u} d u}}}}{5} = 2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x} - \frac{\sqrt{5} {\color{red}{\ln{\left(\left|{u}\right| \right)}}}}{5}$$

Muista, että $$$u=x - \sqrt{5}$$$:

$$- \frac{\sqrt{5} \ln{\left(\left|{{\color{red}{u}}}\right| \right)}}{5} + 2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x} = - \frac{\sqrt{5} \ln{\left(\left|{{\color{red}{\left(x - \sqrt{5}\right)}}}\right| \right)}}{5} + 2 \int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x}$$

Sovella vakiokertoimen sääntöä $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ käyttäen $$$c=\frac{\sqrt{5}}{10}$$$ ja $$$f{\left(x \right)} = \frac{1}{x + \sqrt{5}}$$$:

$$- \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + 2 {\color{red}{\int{\frac{\sqrt{5}}{10 \left(x + \sqrt{5}\right)} d x}}} = - \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + 2 {\color{red}{\left(\frac{\sqrt{5} \int{\frac{1}{x + \sqrt{5}} d x}}{10}\right)}}$$

Olkoon $$$u=x + \sqrt{5}$$$.

Tällöin $$$du=\left(x + \sqrt{5}\right)^{\prime }dx = 1 dx$$$ (vaiheet ovat nähtävissä ») ja saamme, että $$$dx = du$$$.

Siis,

$$- \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + \frac{\sqrt{5} {\color{red}{\int{\frac{1}{x + \sqrt{5}} d x}}}}{5} = - \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + \frac{\sqrt{5} {\color{red}{\int{\frac{1}{u} d u}}}}{5}$$

Funktion $$$\frac{1}{u}$$$ integraali on $$$\int{\frac{1}{u} d u} = \ln{\left(\left|{u}\right| \right)}$$$:

$$- \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + \frac{\sqrt{5} {\color{red}{\int{\frac{1}{u} d u}}}}{5} = - \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + \frac{\sqrt{5} {\color{red}{\ln{\left(\left|{u}\right| \right)}}}}{5}$$

Muista, että $$$u=x + \sqrt{5}$$$:

$$- \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + \frac{\sqrt{5} \ln{\left(\left|{{\color{red}{u}}}\right| \right)}}{5} = - \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + \frac{\sqrt{5} \ln{\left(\left|{{\color{red}{\left(x + \sqrt{5}\right)}}}\right| \right)}}{5}$$

Näin ollen,

$$\int{\frac{2}{5 - x^{2}} d x} = - \frac{\sqrt{5} \ln{\left(\left|{x - \sqrt{5}}\right| \right)}}{5} + \frac{\sqrt{5} \ln{\left(\left|{x + \sqrt{5}}\right| \right)}}{5}$$

Sievennä:

$$\int{\frac{2}{5 - x^{2}} d x} = \frac{\sqrt{5} \left(- \ln{\left(\left|{x - \sqrt{5}}\right| \right)} + \ln{\left(\left|{x + \sqrt{5}}\right| \right)}\right)}{5}$$

Lisää integrointivakio:

$$\int{\frac{2}{5 - x^{2}} d x} = \frac{\sqrt{5} \left(- \ln{\left(\left|{x - \sqrt{5}}\right| \right)} + \ln{\left(\left|{x + \sqrt{5}}\right| \right)}\right)}{5}+C$$

$$$\int \frac{2}{5 - x^{2}}\, dx = \frac{\sqrt{5} \left(- \ln\left(\left|{x - \sqrt{5}}\right|\right) + \ln\left(\left|{x + \sqrt{5}}\right|\right)\right)}{5} + C$$$A