Mathematics · Grades 7–10
Area of a circle
Use the radius, not the diameter. These exercises request the coefficient of π.
The key idea
Use the radius, not the diameter. These exercises request the coefficient of π.
A = πr²
Worked examples
A circle has radius 27 cm. Its area is kπ cm². Find k.
A = π × 27² = 729π → k = 729
729
A circle has radius 10 cm. Its area is kπ cm². Find k.
A = π × 10² = 100π → k = 100
100
Try it yourself
A circle has radius 57 cm. Its area is kπ cm². Find k.
A circle has radius 7 cm. Its area is kπ cm². Find k.
Check your understanding
Answers and marking notes
- 3249
A = π × 57² = 3249π → k = 3249
- 49
A = π × 7² = 49π → k = 49
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.