The area of the sector FDA is 4pi, and the area of the triangle FBC is 4*12/2=24

According to the similarity of triangles, The area of the small triangle in the sector FDA is 24/9=8/3

, so the shadow area in the sector FDA is 4pi-8/3

The area of the triangle in the shadow part on the right side is 8*(8/3)/2=32/3

, so the total shadow area is 4pi+8

2. Join AO and BO

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