The product of radii of two circles through a point

Question

The problem is the number 4 on the section 1.1 of Coxeter's Revisited Geometry, it says:

Let p and q be the radii of two circles through A, touching BC at B and C, respectively. Then $pq = R^2$.

I've already found its demonstration. I actually need somebody to show me how it looks in plane.

Answer 1

Hope this helps.....................