r=28 A=28*2pi=784pim2
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Raggio $r = \dfrac{c}{2\pi} = \dfrac{56\pi}{2\pi} = \dfrac{56\cancel{\pi}}{2\cancel{\pi}} = 28\,m;$
area $A= r^2·\pi = 28^2·\pi = 784\pi\,m^2.$
area A = π*d^2/4= π*34^2/4 = 289π cm^2
area A = π*r^2
raggio r = √A/π = √(2.704 π/π) = 52,0 cm
raggio r = 56/2 = 28 m
area A = π*28^2 = 784π m^2