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The area of the shadow in the figure below is 50 square centimeters, and the ring area can be calculated
[analysis and answer] the area of the ring should be the area of the big circle minus the area of the small circle. But it is impossible to calculate the area of the big circle and the small circle separately. The area of the shaded part in the figure is the area of the big square and the area of the small square
That is r2-r2 = 50cm2
The area of the ring = л R2 - л R2
＝л(R2－r2)
＝50л
＝157(cm2)
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