Integral of $$$\frac{\sin{\left(r \right)}}{r}$$$

Find $$$\int \frac{\sin{\left(r \right)}}{r}\, dr$$$.

This integral (Sine Integral) does not have a closed form:

$${\color{red}{\int{\frac{\sin{\left(r \right)}}{r} d r}}} = {\color{red}{\operatorname{Si}{\left(r \right)}}}$$

Therefore,

$$\int{\frac{\sin{\left(r \right)}}{r} d r} = \operatorname{Si}{\left(r \right)}$$

Add the constant of integration:

$$\int{\frac{\sin{\left(r \right)}}{r} d r} = \operatorname{Si}{\left(r \right)}+C$$

$$$\int \frac{\sin{\left(r \right)}}{r}\, dr = \operatorname{Si}{\left(r \right)} + C$$$A