Question

The Radius of a sphere is 5 feet. find the area of the great circle of this sphere 

Answer 1

Calculate the area of the great circle, if we substitute for r = 5, since only then the circuit will be the greatest.
$\pi*r^2=3,14*5^2=78,5(ft^2)$

Answer 2

$The\ radius\ of\ a\ sphere\ is\ equal\ the\ radius\ of\ the\ great\ circle\ of\ this\ sphere\\\\R=5ft\\\\A_{O}=\pi R^2\Rightarrow A_O=\pi\times5^2=25\pi\ (ft^2)$