Answer :
A = pi r^2
d = 2r
r= d/2
A = pi (d/2)^2
A = pi d^2/4
4A = pi d^2
d^2 = 4A/pi
d = sqrt(4A/pi)
d = 2 sqrt(A/pi)
d = 2r
r= d/2
A = pi (d/2)^2
A = pi d^2/4
4A = pi d^2
d^2 = 4A/pi
d = sqrt(4A/pi)
d = 2 sqrt(A/pi)