Figure 1: Three circles.
The area of the green outer circle is D = πr2 = π for r = 1. The two cyan inner circles have r = 1∕2 so their areas are D′ = π(1∕2)2 = π∕4 = D∕4. The region outside the two small circles but inside the large circle, shaped somewhat like an Alaskan Ulu knife, has two parts. Each green part has an area the same as a cyan circle, D∕4. This is not obvious to the eye as a cyan region appears larger than a green circle!