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

Area of parts of circles - Answers

1. The answer

The area of the shape is 3 \pi units ^{2}.

(Note that we could also multiply 3 by 3.14 to get 9.42 units ^{2}.)

2. The answer

The area of the semicircle is 12.5 \pi units ^{2}.

(Note that we could also multiply 12.5 by 3.14 to get 39.25 units ^{2}.)

3. The answer

The area of the semicircle is 4.5 \pi units ^{2}.

(Note that we could also multiply 4.5 by 3.14 to get 14.13 units ^{2}.)

4. The answer

The area of the shape is 12 \pi units ^{2}.

(Note that we could also multiply 12 by 3.14 to get 37.68 units ^{2}.)