You can find the circumference of a circle using pi (π) with either of two simple formulas: C = πd or C = 2πr, where 'C' is the circumference, 'd' is the diameter, and 'r' is the radius.
Here's a breakdown of how to use each formula:
1. Using the Diameter (C = πd):
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The diameter (d) of a circle is the distance across the circle through its center.
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Pi (π) is a mathematical constant approximately equal to 3.14159. For most calculations, you can use 3.14.
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To find the circumference, simply multiply the diameter by pi.
- Example: If a circle has a diameter of 5 cm, its circumference would be C = π 5 cm = approximately 3.14 5 cm = 15.7 cm.
2. Using the Radius (C = 2πr):
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The radius (r) of a circle is the distance from the center of the circle to any point on its edge. It's half the length of the diameter.
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To find the circumference, multiply 2 by pi and then by the radius.
- Example: If a circle has a radius of 3 inches, its circumference would be C = 2 π 3 inches = approximately 2 3.14 3 inches = 18.84 inches.
In Summary:
| Formula | Description | Variables |
|---|---|---|
| C = πd | Circumference equals pi times the diameter. | C = Circumference, π = Pi, d = Diameter |
| C = 2πr | Circumference equals two times pi times the radius. | C = Circumference, π = Pi, r = Radius |
Both formulas are mathematically equivalent since the diameter is twice the radius (d = 2r). Choose the formula that best suits the information you have available (diameter or radius).
