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 a Missing Angle in a Triangle Find the third angle when two angles are 65 and 48 degrees. Three steps, the 180-degree reason, and the mistakes to avoid.
- How to Use the Pythagorean Theorem Find the hypotenuse of a right triangle with legs 6 and 8. Three steps, the theorem, and the square and root mistakes to avoid.
Practice this topic
3 problems with answers.