V1一个大圆里面切了一个小圆，说小圆的outside diameter is equal to inside radius of the large circular. And the cross-section area of the large circular is 49pai, what is the cross-section area of the small circular?
think of it as a Donut. The area of the big circle is 49pai. So the radius of big circle is 7.
Since the outside diameter of small circle is equal to the radius of the big circle, then u have 7/2 as the radius of the small circle. Now u can find the area of the small circle.
pai*(7/2)^2 = area of small circle.
Once more thing, another question gives u the area of the big cirlce as 14pai instead of 49pai
o sorry, it is not a donut, but a small circle inside a big circle. For example, big circle has points (4,0)(0,4)(-4,0)(0-4). small circle has points (4,0)(0,0)(2,2) (-2,-2).
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发表于 2009-2-22 13:55:00
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