91�ȱ�

The circumference of a circle is calculated using the formula: \(\text{circumference} = \pi \times \text{diameter}\), which can be written as \(\text{c} = \pi \text{d}\)

Or: \(\text{circumference} = 2 \times \pi \times \text{radius}\), which can be written as \(\text{c} = 2\pi \text{r}\)

\(\text{circumference} \div \text{diameter} = 3.1415 \dotsc\)

\(\pi = 3.1415926535897932384626433832795 \dotsc\)

The pi symbol (\(\pi\)) allows you to give the exact value to a calculation involving circles as pi cannot be written as an exact fraction or decimal. If a decimal answer is required, the value can be approximated as 3.14 (3 significant figures).

Scientific calculators have a \(\pi\) button which can be used during calculations.

\(d = 20 \times 2 = 40~\text{cm}\)

Using \(\text{circumference} = \pi \text{d}\)

Circumference = \(\pi \times 40 = 125.7~\text{cm}\) (1 decimal place).

The answer can also be given in terms of \(\pi\). In this case the answer is \(40 \pi~\text{cm}\).