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Year 8 · Measurement

Circumference and area of circles

Circumference is the distance around a circle; area is the space inside. Both use π ≈ 3.14.

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How to do it

  1. Circumference = 2 × π × radius.
  2. Area = π × radius × radius.

Worked example

A circle has a radius of 9 cm. Using π ≈ 3.14, what is its circumference, in cm? Give one decimal place.
Circumference = 2πr = 2 × 3.14 × 9 = 56.5.
Answer: 56.5

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Use the radius, which is half the diameter.

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