Answer:
Area = πr²
Circumference = 2πr
Explanation:
When given the radius r ,
Area of a circle A = πr²
Circumference of the circle C = 2πr
When given diameter d,
Area of a circle A = πd²/4
Circumference of a circle = πd
To find the radius r and d from area A,
r = sqrt(A/π)
d = sqrt(4A/π)
To find the radius r and diameter d from a given circumference C,
r = C/(2π)
d = C/π
Where d = 2r