Integral of $$$3 x^{2} - 4 x$$$

Find $$$\int \left(3 x^{2} - 4 x\right)\, dx$$$.

Integrate term by term:

$${\color{red}{\int{\left(3 x^{2} - 4 x\right)d x}}} = {\color{red}{\left(- \int{4 x d x} + \int{3 x^{2} d x}\right)}}$$

Apply the constant multiple rule $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ with $$$c=4$$$ and $$$f{\left(x \right)} = x$$$:

$$\int{3 x^{2} d x} - {\color{red}{\int{4 x d x}}} = \int{3 x^{2} d x} - {\color{red}{\left(4 \int{x d x}\right)}}$$

Apply the power rule $$$\int x^{n}\, dx = \frac{x^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ with $$$n=1$$$:

$$\int{3 x^{2} d x} - 4 {\color{red}{\int{x d x}}}=\int{3 x^{2} d x} - 4 {\color{red}{\frac{x^{1 + 1}}{1 + 1}}}=\int{3 x^{2} d x} - 4 {\color{red}{\left(\frac{x^{2}}{2}\right)}}$$

Apply the constant multiple rule $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ with $$$c=3$$$ and $$$f{\left(x \right)} = x^{2}$$$:

$$- 2 x^{2} + {\color{red}{\int{3 x^{2} d x}}} = - 2 x^{2} + {\color{red}{\left(3 \int{x^{2} d x}\right)}}$$

Apply the power rule $$$\int x^{n}\, dx = \frac{x^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ with $$$n=2$$$:

$$- 2 x^{2} + 3 {\color{red}{\int{x^{2} d x}}}=- 2 x^{2} + 3 {\color{red}{\frac{x^{1 + 2}}{1 + 2}}}=- 2 x^{2} + 3 {\color{red}{\left(\frac{x^{3}}{3}\right)}}$$

Therefore,

$$\int{\left(3 x^{2} - 4 x\right)d x} = x^{3} - 2 x^{2}$$

Simplify:

$$\int{\left(3 x^{2} - 4 x\right)d x} = x^{2} \left(x - 2\right)$$

Add the constant of integration:

$$\int{\left(3 x^{2} - 4 x\right)d x} = x^{2} \left(x - 2\right)+C$$

$$$\int \left(3 x^{2} - 4 x\right)\, dx = x^{2} \left(x - 2\right) + C$$$A