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MathGroup Archive 1998

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Fast help for circle problem

  • To: mathgroup at
  • Subject: [mg13261] Fast help for circle problem
  • From: jmittag <jmittag at>
  • Date: Fri, 17 Jul 1998 03:17:53 -0400
  • Organization: Technical University Berlin, Germany
  • Sender: owner-wri-mathgroup at

We are looking for a solution for the following problem:

Given are 3 circles, each with center coordinates and radius. Circle 1
is touching circle 2 and circle 2 is touching circle 3 (without any
intersection). As a special case circle 1 is also touching circle 3.

We are looking for circle 4, which is touching circles 1 to 3.

The equation for one circle "i" is as follows:

(ri+r4)^2=(x4-xi)^2+(y4-yi)^2   with i = 1,2,3

We need a symbolic solution for x4, y4 and r4.

Thanks in advance!

Jens Mittag

email: Jens.Mittag at

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