Integral dari $$$x^{2} \cos{\left(x \right)}$$$

Temukan $$$\int x^{2} \cos{\left(x \right)}\, dx$$$.

Untuk integral $$$\int{x^{2} \cos{\left(x \right)} d x}$$$, gunakan integrasi parsial $$$\int \operatorname{u} \operatorname{dv} = \operatorname{u}\operatorname{v} - \int \operatorname{v} \operatorname{du}$$$.

Misalkan $$$\operatorname{u}=x^{2}$$$ dan $$$\operatorname{dv}=\cos{\left(x \right)} dx$$$.

Maka $$$\operatorname{du}=\left(x^{2}\right)^{\prime }dx=2 x dx$$$ (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

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

Terapkan aturan pengali konstanta $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ dengan $$$c=2$$$ dan $$$f{\left(x \right)} = x \sin{\left(x \right)}$$$:

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

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

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

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

Dengan demikian,

$$x^{2} \sin{\left(x \right)} - 2 {\color{red}{\int{x \sin{\left(x \right)} d x}}}=x^{2} \sin{\left(x \right)} - 2 {\color{red}{\left(x \cdot \left(- \cos{\left(x \right)}\right)-\int{\left(- \cos{\left(x \right)}\right) \cdot 1 d x}\right)}}=x^{2} \sin{\left(x \right)} - 2 {\color{red}{\left(- x \cos{\left(x \right)} - \int{\left(- \cos{\left(x \right)}\right)d x}\right)}}$$

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

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

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

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

Oleh karena itu,

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

Tambahkan konstanta integrasi:

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

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