Circles

You can use pi to calculate the circumference and area of a circle. Pi is represented by the symbol π and is a number which is approximately 3.141592.

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What is pi?

For any circle, $circumference \div diameter = 3.141592...$

Portrait of mathematician Sir William Jones, by the artist William Hogarth, 1740

Credit: © NPG

Portrait of Welsh mathematician, Sir William Jones (1675 - 1749) by the artist William Hogarth

This number is so special that it is given its own symbol $\pi$ (the Greek letter pi).

The value $\pi$ is a constant, but is called an irrational number as an exact value for $\pi$ does not exist. In non-calculator working out, approximate values are used, of which 3.14 and 3.142 are probably the most common. Other, less accurate approximations are $\frac{22}{7}$ and .

All scientific calculators have a $\pi$ button. You can use this to make your calculations more accurate.

The earliest known use of the Greek letter $\pi$ , to represent the ratio of a circle's circumference to its diameter, was by the Welsh mathematician William Jones in his 1706 work ‘Synopsis Palmariorum Matheseos’ or, ‘A New Introduction to the Mathematics’.

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Circles

What is pi?

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