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Circles

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Information

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Introducing circles

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Naming the parts of a circle

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Circumference and diameter

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For any circle, the circumference is always just over three times bigger than the radius.

The exact number is called π (pi).

We use the symbol π because the number cannot be written exactly.

π = 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651328230664709384460955058223172535940812848111745028410270193852110555964462294895493038196… (to 200 decimal places)

The value of π

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A useful approximation is 3.14 or 22/7

We can also use the π button on a calculator.

Most questions will tell you which approximation to use.

Approximate values of pi

When a calculation has lots of steps, we write pi as a symbol throughout and evaluate it at the end.

When we are doing calculations involving π we need to use an approximation for the value.

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How can we rearrange this formula to make a formula for the circumference of a circle?

C = π d

For any circle: π =circumference

diameter =

dC

A formula for circumference

circumference = π × diameter

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Circumference problem