Because OA=OB, Angel OAB= Angel OBC? Angle AOE= Angle BOF(ASA)

Triangle AOE is the same as triangle BOF, so shadow BOF can be filled into triangle AOE.

So the area of the shaded part is the area of the triangle AOB.

The area of triangle AOB is 0/4 of 65438+ square ABCD.

So s shadow =2*2/4= 1.