geometry formulas for area and perimeter of shapes

Circle sector

circle area and perimeter formula
$$\textbf{Area of the circle sector}$$
$$A = r^2 \theta,$$
$$where \; \theta \; is \; in \; radian$$
$$\textbf{Arc length}$$
$$s = r \theta,$$
$$where \; \theta \; is \; in \; radian$$
$$If \; \;\theta \; is \; in \; degree \; s = {\theta\over 360} 2 \pi r$$