# Area and circumference of circles

1 article
3 videos
3 skills
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

VIDEO 11:05 minutes
Learn how the number Pi allows us to relate the radius, diameter, and circumference of a circle.

### Labeling parts of a circle

VIDEO 2:01 minutes
Radius, diameter, center, and circumference--all are parts of a circle. Let's go through each and understand how they are defined.

ARTICLE
Walk through understanding the relationship between the radius, diameter, and circumference of a circle.

PRACTICE PROBLEMS
Practice finding the radius, diameter, or circumference of a circle. For example, if the diameter of a circle is 16, what is its circumference?

### Area of a circle

VIDEO 4:02 minutes
In this example, we solve for the area of a circle when given the diameter. If you recall, the diameter is the length of a line that runs across the circle and through the center.

### Area of a circle

PRACTICE PROBLEMS

### Area and circumference of parts of circles

PRACTICE PROBLEMS
Practice finding the area or circumference of part of a circle.