It’s in other sports too, so cycling, for example, the wheels are ... Image caption, The diameter is the whole distance across the circle, through its centre. The diameter is two radii.

The diameter of the circle is given an arbitrary value of 1 ... in Archimedes' day—Archimedes used geometry instead. For example, he knew the ratio between one line and another in certain ...

To work out the area of a circle: Find the value of the radius. If the diameter is given, this must be halved. Substitute the value of the radius into the formula for the area of a circle.