As in figure 2.In the circular 
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As in figure 2.In the circular ring of which center is point O.if AO⊥BO,and the area of the shadowy part is 25cm2,then the area of the circuiar ring equals to( ) (π≈3.14)
A. 147cm2
B. 157cm2
C. 167cm2
D. 177cm2
A. 147cm2
B. 157cm2
C. 167cm2
D. 177cm2
设大圆的半径为R,小圆的半径为r,
∵AO⊥BO,
∴阴影的面积为两个直角三角形的面积之差,
∴R2-r2=50,
∵圆环的面积为两个圆的面积之差,
∴圆环的面积=π(R2-r2)=50π=157cm2.
故选B.
∵AO⊥BO,
∴阴影的面积为两个直角三角形的面积之差,
∴R2-r2=50,
∵圆环的面积为两个圆的面积之差,
∴圆环的面积=π(R2-r2)=50π=157cm2.
故选B.
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