Integral of $$$- 3 \cos{\left(x \right)}$$$

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

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

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

The integral of the cosine is $$$\int{\cos{\left(x \right)} d x} = \sin{\left(x \right)}$$$:

$$- 3 {\color{red}{\int{\cos{\left(x \right)} d x}}} = - 3 {\color{red}{\sin{\left(x \right)}}}$$

Therefore,

$$\int{\left(- 3 \cos{\left(x \right)}\right)d x} = - 3 \sin{\left(x \right)}$$

Add the constant of integration:

$$\int{\left(- 3 \cos{\left(x \right)}\right)d x} = - 3 \sin{\left(x \right)}+C$$

$$$\int \left(- 3 \cos{\left(x \right)}\right)\, dx = - 3 \sin{\left(x \right)} + C$$$A