# Concentric Circles

Two circles are concentric if their centers coincide. The area enclosed between two concentric circles are also referred to as the **annulus **or **circular ring**.

#### Area of the Annulus

The area of the annulus equals the area of the larger circle minus the area of smaller circle.

### Circular Trapezoid

The circular trapezoid is the area enclosed within two radii and two concentric circles.

#### Area of a Circular Trapezoid

The area of the circular trapezoid is equal to area of the the largest circular sector minus the area of the smaller circular sector.

#### Examples

A circular fountain of 5 m radius lies alone in the centre of a circular park of 700 m radius. Calculate the total walking area available to pedestrians visiting the park.

Calculate the area enclosed by the inscribed and circumscribed circles to a square with a diagonal of 8 m in length.

A regular hexagon of side 4 cm has a circle inscribed and another circumscribed around its shape. Find the area enclosed between these two concentric circles.

Two radii (plural for radius) OA and OB form an angle of 60° for two concentric circles with 8 and 5 cm radii. Calculate the area of the circular trapezoid formed by the radii and concentric circles.