And ∵S great circle = half XπXR?

S small circle = half XπXr?

∴ Half and π are gone, r? ，r？ Both are squares, because 1X 1= 1 is small and 3X3=9 is big.

We can get the radius of the big circle: the radius of the small circle = 3: 1,

The radius ratio of two circles is d.

Simply put, it is like this:

1/9= 1/3× 1/3

So the radius ratio of two circles is 3: 1.