The formula for the area of a circle, A, in terms of its radius, r, is:
A = πr2
We can rearrange this formula to make r the subject.
The formula for the radius of a circle, r, in terms of its area, A, is:
Calculate the radius, r cm, of a circle which has an area of 100 cm2.
Give your answer to 3 sig. figs.
r2 = 100 ÷ π = 31.831
r = √31.831 = 5.641896 ≈ 5.64 cm (3 s.f.)