Area and circumference of circles

A circle is at the foundation of geometry, and at the foundation of a circle is a special number called Pi. This number allows us to relate the radius, diameter, and circumference of a circle.

Radius, diameter, circumference & π

Labeling parts of a circle

Radius and diameter

Radius & diameter from circumference

Relating circumference and area

Circumference of a circle

Area of a circle

Area of a circle

Partial circle area and arc length

Circumference of parts of circles

Area of parts of circles