Circumference and area of circles

4 videos
4 skills
Circles are everywhere. How can we measure how big they are? Well, we could think about the distance around the circle (circumference). Another option would be to think about how much space it takes up on our paper (area). Have fun!

Circles: radius, diameter, circumference and Pi

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

Radius, diameter, and circumference

Practice labeling the parts of a circle: radius, diameter, and 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


Shaded areas

Find the areas of shaded regions which are combinations of squares, triangles, and circles.

Example: Solving for the radius or diameter from circumference

VIDEO 3:36 minutes
Sal finds the radius and diameter of a circle given the circumference.

Solving for the radius or diameter from circumference

You'll be given the circumference or the area of a circle, and it will be up to you to figure out the radius or the diameter.

Informal argument for the area of circle formula

VIDEO 9:26 minutes
Using triangles to create an informal argument for the area of a circle formula.