In the sequel [XYZ] will represent the area of a triangle XYZ. Denote by S the area of the polygon A1A2...A2010.
Notice that [OA1A2]=[OA2A3]=⋯=[OA2010A1]=20101S, since the polygon A1A2...A2010 is given as being regular. Then for each k=1,2,...,2009 we have
[OAkAk+1][OBkBk+1]=OAk⋅OAk+1OBk⋅OBk+1=k(k+1)1,
as well as
[OA2010A1][OB2010B1]=OA2010⋅OA1OB2010⋅OB1=20101,
since the ratio of the areas of two triangles sharing a same angle is equal to the ratio of the products of the corresponding sides.
Therefore denoting by T the area of the polygon B1B2...B2010, we have
T=k=1∑2009[OBkBk+1]+[OB2010B1]=2010S(k=1∑2009k(k+1)1+20101)=2010S(k=1∑2009(k1−k+11)+20101)=2010S((1−20101)+20101)=2010S,
hence ST=20101.