Răspuns:
Explicație pas cu pas:
A = πR^2
R^2 = A : π
D = 2 x R
______
A = 100π m^2
R^2 = 100π : π = 100
R = 10 m
D = 2 x 10 = 20 m
__________
A = 25π m^2
R^2 = 25π : π = 25
R = 5 m
D = 2 x 5 = 10 m
_____________
A = 100 m^2
R^2 = 100/π
R = 10/√π = 10√π/π m
D = 2 x 10√π/π = 20√π/π m