https://decimal-to-binary.com/ploschad-sector-ring.html?id=2

Method of calculating the area of the ring sector:

Radius R: Radius r: Angle α°:

Diameter D: Diameter d: Angle α°:

The sector of the ring is the part of the circle that is bounded by the inner and outer arc of this ring and the two outer radii of this ring.
Formula of the area of the ring sector where R is the radius of the outer circle, r is the radius of the inner circle, α° is the angle between the radii of the ring.

The sector of the ring is the part of the circle that is bounded by the inner and outer arc of this ring and the two outer radii of this ring.
Formula of the area of the ring sector where D is the diameter of the outer circle, d is the diameter of the inner circle, α° is the angle between the radii of the ring.

Solution: