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Lesson: Geometry Challenging - 05

Finding A Circumference

[Page 5 of 32]

Pi (symbolized by Π) is the ratio of a circle's circumference to its diameter. The value of Π is approximately 3.14.

To find the circumference of a circle, multiply its diameter by Π. Since the diameter is twice the radius, the circumference equals 2Π times the radius, or 2Π r.

In the figure above, W is the center of the circle, and WX = 9. The circumference is 2Π r or 2Π(9) = 18Π.

Most questions will leave the Π symbol in the answer choices. If Π isn't in the answer choices, you can approximate it as 3, or 3.14 if you need more precision.

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