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1/4 area of the great circle (integer): 3.14× 20× 20×1/4 = 314cm2.

The area of a small semicircle (diameter 20cm): 3.14× (20/2 )× (20/2) ÷ 2 =157cm2.

The area of overlapping shadow of two small semicircles is: 157-20×(20/2)÷2=57 cm2.

(Hint: You can divide the shadow like a leaf in the middle into two parts evenly, and then turn it over to make it in a whole circle. After careful observation, it is easy to understand why this is so. )

The shadow area of the other part is: 314-157× 2+57 = 57cm2.

(Note: When the area of a whole circle (two small semicircles) is subtracted from the area of 1/4 big circle (the whole figure), the area of the overlapping shadow part is reduced again, so it is added back to 57 square centimeters. )

Therefore, the total area of the shadow area is: 57+57= 1 14 cm2.