Mathematics for IGCSE & O level - Mensuration (Section 11 - No. 19)
What is the relationship between the radius (r) and the diameter (d) of a circle?
r = d / 2
d = 2r
r = 2d
d = r / 2
解释
The radius is half the diameter (r = d/2), and the diameter is twice the radius (d = 2r).