Answer: Radius is always half the length of its diameter. For example, if the diameter is 4 cm, the radius equals 4 cm ÷ 2 = 2 cm.
When the diameter is known, the formula is Radius = Diameter/ 2.
When the circumference is known, the formula is Radius = Circumference/2π.
When the area is known, the formula for the radius is Radius = ⎷(Area of the circle/π).
The radius of a circle from diameter: if you know the diameter d , the radius is r = d / 2
The value of Pi (π) is the ratio of the circumference of a circle to its diameter and is approximately equal to 3.14159.
Explanation: