Geometry · Grades 9 to 10
Circles and area
Find the area of a circle from its radius.
The idea
The area of a circle is the space inside its edge. It depends on the radius: A = πr².
The radius is half the diameter. Keep the answer in terms of π for an exact value, or use 3.14 for an estimate.
Worked examples
- How to Find the Area of a Circle Find the area of a circle with radius 5. Four steps with A = pi r^2, the exact answer in terms of pi, and the mistakes to avoid.
- How to Find the Circumference of a Circle Find the circumference of a circle with radius 7. Four steps with C = 2 pi r, the exact answer in terms of pi, and the radius mistakes to avoid.
- How to Find the Area of a Circle from the Diameter Find the area of a circle with diameter 12. Four steps that halve the diameter first, apply A = pi r^2, and avoid the diameter mistakes.
Practice this topic
3 problems with answers.