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 proof by Charlie)

Don't you also have to show that BS is parallel to PAR before you can say that ASBR is a parallelogram?

Clearly, the argument is similar to showing AS is parallel to QBR.

Posted by Bractals on 2009-07-14 01:16:25