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Collinear intersections (Posted on 2009-07-13) Difficulty: 2 of 5
Two smaller circles of radii a and b are internally tangent to a larger circle, of radius r, at points P and Q respectively. The smaller circles intersect at points S and T.

If P, S, and Q are collinear, prove that r = a+b.

See The Solution Submitted by Bractals    
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re(2): proof Comment 3 of 3 |
(In reply to re: proof by Bractals)

Right: as all three triangles are similar, angle SBQ = angle PRQ and so BS is parallel to PAR.
  Posted by Charlie on 2009-07-14 02:34:14

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