Funktion $$$\frac{1}{\sin{\left(x \right)} \tan{\left(x \right)}}$$$ integraali

Määritä $$$\int \frac{1}{\sin{\left(x \right)} \tan{\left(x \right)}}\, dx$$$.

Olkoon $$$u=\sin{\left(x \right)}$$$.

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

Siis,

$${\color{red}{\int{\frac{1}{\sin{\left(x \right)} \tan{\left(x \right)}} d x}}} = {\color{red}{\int{\frac{1}{u^{2}} d u}}}$$

Sovella potenssisääntöä $$$\int u^{n}\, du = \frac{u^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ käyttäen $$$n=-2$$$:

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

Muista, että $$$u=\sin{\left(x \right)}$$$:

$$- {\color{red}{u}}^{-1} = - {\color{red}{\sin{\left(x \right)}}}^{-1}$$

Näin ollen,

$$\int{\frac{1}{\sin{\left(x \right)} \tan{\left(x \right)}} d x} = - \frac{1}{\sin{\left(x \right)}}$$

Lisää integrointivakio:

$$\int{\frac{1}{\sin{\left(x \right)} \tan{\left(x \right)}} d x} = - \frac{1}{\sin{\left(x \right)}}+C$$

$$$\int \frac{1}{\sin{\left(x \right)} \tan{\left(x \right)}}\, dx = - \frac{1}{\sin{\left(x \right)}} + C$$$A