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.

(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