Integral dari $$$x \sin{\left(5 \right)} \cos{\left(x \right)}$$$

Temukan $$$\int x \sin{\left(5 \right)} \cos{\left(x \right)}\, dx$$$.

Terapkan aturan pengali konstanta $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ dengan $$$c=\sin{\left(5 \right)}$$$ dan $$$f{\left(x \right)} = x \cos{\left(x \right)}$$$:

$${\color{red}{\int{x \sin{\left(5 \right)} \cos{\left(x \right)} d x}}} = {\color{red}{\sin{\left(5 \right)} \int{x \cos{\left(x \right)} d x}}}$$

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

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

Maka $$$\operatorname{du}=\left(x\right)^{\prime }dx=1 dx$$$ (langkah-langkah dapat dilihat di ») dan $$$\operatorname{v}=\int{\cos{\left(x \right)} d x}=\sin{\left(x \right)}$$$ (langkah-langkah dapat dilihat di »).

Integral tersebut dapat ditulis ulang sebagai

$$\sin{\left(5 \right)} {\color{red}{\int{x \cos{\left(x \right)} d x}}}=\sin{\left(5 \right)} {\color{red}{\left(x \cdot \sin{\left(x \right)}-\int{\sin{\left(x \right)} \cdot 1 d x}\right)}}=\sin{\left(5 \right)} {\color{red}{\left(x \sin{\left(x \right)} - \int{\sin{\left(x \right)} d x}\right)}}$$

Integral dari sinus adalah $$$\int{\sin{\left(x \right)} d x} = - \cos{\left(x \right)}$$$:

$$\sin{\left(5 \right)} \left(x \sin{\left(x \right)} - {\color{red}{\int{\sin{\left(x \right)} d x}}}\right) = \sin{\left(5 \right)} \left(x \sin{\left(x \right)} - {\color{red}{\left(- \cos{\left(x \right)}\right)}}\right)$$

Oleh karena itu,

$$\int{x \sin{\left(5 \right)} \cos{\left(x \right)} d x} = \left(x \sin{\left(x \right)} + \cos{\left(x \right)}\right) \sin{\left(5 \right)}$$

Tambahkan konstanta integrasi:

$$\int{x \sin{\left(5 \right)} \cos{\left(x \right)} d x} = \left(x \sin{\left(x \right)} + \cos{\left(x \right)}\right) \sin{\left(5 \right)}+C$$

$$$\int x \sin{\left(5 \right)} \cos{\left(x \right)}\, dx = \left(x \sin{\left(x \right)} + \cos{\left(x \right)}\right) \sin{\left(5 \right)} + C$$$A