The answer process is as follows:
(1) According to the fact that the radius of the great circle is twice that of the small circle, if the radius of the small circle is r, the radius of the great circle is 2r.
(2) According to the fact that the area of a big circle is more than that of a small circle 12cm2, we can get: π(2r)? -πr？ = 12 cm2。
(3)π(2r)？ -πr？ = 12 cm2, simplified as: 3πr? = 12 cm2。
(4) The area of the small circle =πr? . Put 3πr? = 12 cm2. Divide both sides of the equation by 3.
(5) Therefore, the area of the small circle = 12/3 = 4cm2.
Extended data:
Formula related to circle:
1, circular area: S=πr? ，S=π(d/2)？ . (d is the diameter and r is the radius).
2. area of semicircle: s semicircle = (π r 2)/2. (r is the radius).
3. Ring area: s great circle -S small circle = π (r 2-r 2) (r is the radius of great circle and r is the radius of small circle).
4. Circumference: C=2πr or c = π d..(d is the diameter and r is the radius).
5. The circumference of a semicircle: d+(πd)/2 or d+π r (d is the diameter and r is the radius).