Integral dari $$$- e^{x} \cos{\left(x \right)}$$$

Temukan $$$\int \left(- e^{x} \cos{\left(x \right)}\right)\, dx$$$.

Terapkan aturan pengali konstanta $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ dengan $$$c=-1$$$ dan $$$f{\left(x \right)} = e^{x} \cos{\left(x \right)}$$$:

$${\color{red}{\int{\left(- e^{x} \cos{\left(x \right)}\right)d x}}} = {\color{red}{\left(- \int{e^{x} \cos{\left(x \right)} d x}\right)}}$$

Untuk integral $$$\int{e^{x} \cos{\left(x \right)} d x}$$$, gunakan integrasi parsial $$$\int \operatorname{u} \operatorname{dv} = \operatorname{u}\operatorname{v} - \int \operatorname{v} \operatorname{du}$$$.

Misalkan $$$\operatorname{u}=\cos{\left(x \right)}$$$ dan $$$\operatorname{dv}=e^{x} dx$$$.

Maka $$$\operatorname{du}=\left(\cos{\left(x \right)}\right)^{\prime }dx=- \sin{\left(x \right)} dx$$$ (langkah-langkah dapat dilihat di ») dan $$$\operatorname{v}=\int{e^{x} d x}=e^{x}$$$ (langkah-langkah dapat dilihat di »).

Dengan demikian,

$$- {\color{red}{\int{e^{x} \cos{\left(x \right)} d x}}}=- {\color{red}{\left(\cos{\left(x \right)} \cdot e^{x}-\int{e^{x} \cdot \left(- \sin{\left(x \right)}\right) d x}\right)}}=- {\color{red}{\left(e^{x} \cos{\left(x \right)} - \int{\left(- e^{x} \sin{\left(x \right)}\right)d x}\right)}}$$

Terapkan aturan pengali konstanta $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ dengan $$$c=-1$$$ dan $$$f{\left(x \right)} = e^{x} \sin{\left(x \right)}$$$:

$$- e^{x} \cos{\left(x \right)} + {\color{red}{\int{\left(- e^{x} \sin{\left(x \right)}\right)d x}}} = - e^{x} \cos{\left(x \right)} + {\color{red}{\left(- \int{e^{x} \sin{\left(x \right)} d x}\right)}}$$

Untuk integral $$$\int{e^{x} \sin{\left(x \right)} d x}$$$, gunakan integrasi parsial $$$\int \operatorname{u} \operatorname{dv} = \operatorname{u}\operatorname{v} - \int \operatorname{v} \operatorname{du}$$$.

Misalkan $$$\operatorname{u}=\sin{\left(x \right)}$$$ dan $$$\operatorname{dv}=e^{x} dx$$$.

Maka $$$\operatorname{du}=\left(\sin{\left(x \right)}\right)^{\prime }dx=\cos{\left(x \right)} dx$$$ (langkah-langkah dapat dilihat di ») dan $$$\operatorname{v}=\int{e^{x} d x}=e^{x}$$$ (langkah-langkah dapat dilihat di »).

Oleh karena itu,

$$- e^{x} \cos{\left(x \right)} - {\color{red}{\int{e^{x} \sin{\left(x \right)} d x}}}=- e^{x} \cos{\left(x \right)} - {\color{red}{\left(\sin{\left(x \right)} \cdot e^{x}-\int{e^{x} \cdot \cos{\left(x \right)} d x}\right)}}=- e^{x} \cos{\left(x \right)} - {\color{red}{\left(e^{x} \sin{\left(x \right)} - \int{e^{x} \cos{\left(x \right)} d x}\right)}}$$

Kita telah sampai pada integral yang sudah pernah kita lihat.

Dengan demikian, kita telah memperoleh persamaan sederhana berikut sehubungan dengan integral:

$$- \int{e^{x} \cos{\left(x \right)} d x} = - e^{x} \sin{\left(x \right)} - e^{x} \cos{\left(x \right)} + \int{e^{x} \cos{\left(x \right)} d x}$$

Dengan menyelesaikannya, kita memperoleh bahwa

$$\int{e^{x} \cos{\left(x \right)} d x} = \frac{\left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) e^{x}}{2}$$

Oleh karena itu,

$$- {\color{red}{\int{e^{x} \cos{\left(x \right)} d x}}} = - {\color{red}{\left(\frac{\left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) e^{x}}{2}\right)}}$$

Oleh karena itu,

$$\int{\left(- e^{x} \cos{\left(x \right)}\right)d x} = - \frac{\left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) e^{x}}{2}$$

Sederhanakan:

$$\int{\left(- e^{x} \cos{\left(x \right)}\right)d x} = - \frac{\sqrt{2} e^{x} \sin{\left(x + \frac{\pi}{4} \right)}}{2}$$

Tambahkan konstanta integrasi:

$$\int{\left(- e^{x} \cos{\left(x \right)}\right)d x} = - \frac{\sqrt{2} e^{x} \sin{\left(x + \frac{\pi}{4} \right)}}{2}+C$$

$$$\int \left(- e^{x} \cos{\left(x \right)}\right)\, dx = - \frac{\sqrt{2} e^{x} \sin{\left(x + \frac{\pi}{4} \right)}}{2} + C$$$A