Pre-AlgebraCircles
Circles
Learn about circles, their properties, and how to calculate their circumference and area.
Circle Basics
Parts of a Circle
- Center: The point from which all points on the circle are equidistant
- Radius: The distance from the center to any point on the circle
- Diameter: A line segment passing through the center, connecting two points on the circle
- Circumference: The distance around the circle
Important Circle Formulas
- Circumference = 2πr (where r is the radius)
- Circumference = πd (where d is the diameter)
- Area = πr²
- Diameter = 2 × radius
Circle Theorems
- The diameter is twice the radius
- All radii in a circle are equal
- A diameter divides a circle into two equal parts
- The ratio of circumference to diameter is π (pi)
Practice Problems
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Quick Tips
- The value of π (pi) is approximately 3.14159.
- The diameter is always twice the length of the radius.
- Area increases with the square of the radius.