Find the diameter and the radius of a circle with a circumference of 465 cm. Give the answer to the nearest centimetre. Use π = 3۰142 or the π button on a calculator. Image caption, ...

Image caption, The diameter is the whole distance across the circle, through its centre. The diameter is two radii. The radius is half of the diameter. The radius is the distance from the centre ...

Today is Pi Day, but you should stop celebrating it and instead use tau as your circle constant. Tau Day — the true holiday — is celebrated on June 28th.

The constant π is traditionally defined as the ratio of a circle's circumference to its diameter. As I pointed out in the first installment of this series, the fact that this is well-defined (i.e ...

Surely everyone remembers that the area of a circle is: Where Pi (π) is of course the number and r is the radius of the circle ... I can make a plot of area vs. diameter squared.