When working with circles it is important to know the following definitions: The radius (r) of a circle is the distance from the centre to the outside of the circle. The diameter (d) of the circle ...

Remember that the perimeter is the distance round the outside. The perimeter of a semicircle is half of the circumference plus the diameter.

It finds an approximation of pi by determining the length of the perimeter of a polygon inscribed within a circle (which is less than the circumference of the circle) and the perimeter of a ...