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 Question from maribie, a student: two circles are concentric. the tangent to the inner circle forms a chord of 12cm in the larger circle. find the area of the "ring" between the two circles?

Hi Maribile,

Suppose that the radius larger circle is $R$ and the radius of the smaller circle is $r.$ Write an expression for the area of the ring between the two circles.

Next look at a diagram of the two circles.

 $AB$ is perpindcular to $CA$, do you see why? What does Pythagoras say about the triangle $ABC?$

Penny

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