Circles

Parts of a CircleQuadrants.jpg

A circumference is the distance around a circle.

A radius is the distance from the centre to any point on the circumference.

A diameter is a chord that passes through the centre.
The length of the diameter is twice the length of the radius.

 

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Pi

π, the Greek letter pi, is a special number often used in calculations involving circles.

The diameter of a circle, if wrapped around the outside of the circle, would fit just over three times.
(π times)

The value of π is approximately 3.14 (to 2 d.p.).
The fraction with the closest value to pi is 22⁄7 or 31⁄7
Pie.gif

 

Perimeter of a Circle

 

The perimeter of a circle is called the circumference

The length of the circumference (C)

C = 2πr

= πd

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Area of a Circle

The area of a circle is given by the formula

A = πr2