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 Post subject: Geometry or Trig questionPosted: Tue, 12 Jun 2012 18:49:42 UTC
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Can someone help me this afternoon? If I draw eighteen concentric circles, each 71 inches wide, that touch each other to form a large circle, what would the radius of the circle be?

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 Post subject: Re: Geometry or Trig questionPosted: Tue, 12 Jun 2012 18:53:19 UTC
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Joined: Wed, 30 Mar 2005 04:25:14 UTC
Posts: 12103
Location: Austin, TX
jimbaumgart wrote:
Can someone help me this afternoon? If I draw eighteen concentric circles, each 71 inches wide, that touch each other to form a large circle, what would the radius of the circle be?

If they are concentric, then they should all be the same circle.

Assuming you mean by "width" the diameter of this circle, then just use the fact that the radius is half of the diameter.

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 Post subject: Re: Geometry or Trig questionPosted: Tue, 12 Jun 2012 19:00:24 UTC
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Topic moved to geometry and trig board.

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 Post subject: Re: Geometry or Trig questionPosted: Tue, 12 Jun 2012 20:55:11 UTC
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Joined: Mon, 19 May 2003 19:55:19 UTC
Posts: 7952
Location: Lexington, MA
Hello, jimbaumgart!

I suspect this is the "pyramid of tires" problem.

Quote:
If I draw eighteen concentric (?) circles, each 71 inches wide,
that touch each other to form a large circle,
what would the radius of the circle be?

Code:
* * *
*           *
*               *
*                 *

*         A         *
*         o         *
*         |     *   *
|           *   R
*        |35.5    *        *
*       |       *               *
*     |     *                 10d   *
* o * - - - - - - - - - - - - - - - - o C
*     |D    *                       *
*       |       *               *
*        |        *        *
|           *
*         |     *   *
*         o         *
*         B         *

*                 *
*               *
*           *
* * *

The centers are and .

In right triangle

Therefore: .

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