Circumference and Area of a Circle

To calculate the circumference (which is like perimeter) and the area of a circle, you need a special irrational number: pi. Pi is the ratio of the circumference of a circle to its diameter. Watch this lecture series to explore the circumference and area of circles, and complete the interactive exercises.

Practice

Radius and diameter - Answers

1. Radius =9 cm

Diameter =18 cm

2. Radius =4.2 cm

Diameter =8.4 cm

3. =16 units



4. =8 units



5. Radius =6.5 cm

Diameter =13 cm

6. Radius =16 cm

Diameter =32 cm

7.  =4 units