Circumference and area of a circle
The circumference is the perimeter of a circle. It is a length and so is measured in \(mm\), \(cm\), \(m\) or \(km\).
An area is measured in square units: \(mm^{2}\), \(cm^{2}\), \(m^{2}\) or \(km^{2}\)
All of these calculations will involve the use of \(\pi\)(Pi)
Some calculators have a \(\pi\) button but you can also use substitute \(\pi = 3.14\).
However the answers for these two ways of dealing with \(\pi\) are slightly different.
Both ways are allowed, so if your answer is slightly different from the answer given for a question then this is acceptable as long as you have rounded correctly for your method.
Circumference of a circle
For any circle with diameter, \(d\), the circumference, \(C\), is found by using the formula \(C = \pi d\)
For this circle:
\(C = \pi d\)
\(= \pi \times 8\)
\(= 25.13cm\)
Remember that, for any circle, the diameter is twice the radius, or \(d = 2r\).
For this circle:
\(Diameter = 2r\)
\(=2\times 3\)
\(=6cm\)
\(C = \pi d\)
\(=\pi\times 6\)
\(= 18.85cm\)
Area of a circle
For any circle with radius, \(r\), the area, \(A\), is found using the formula \(A = \pi {r^2}\).
For this circle:
\(A = \pi {r^2}\)
\(= \pi \times 3 \times 3\)
\(= 28.27c{m^2}\)
