If A is internally tangent to B and the center of the small circle is at the right angle, the distance between their centers is 10, the longer leg is 20+r where r is the radius of C, and the hypotenuse is 30r, so: 10^2+(20+r)^2 = (30r)^2; this makes r = 4.
If the center of the large circle is the right angle, then 10^2+(30r)^2 = (20+r)^2; thus r = 6.
If A and B are externally tangent and both are external to C, A and B are separated by 50 units.
The center of C will then be at a right angle of the formed triangle if (20+r)^2 + (30+r)^2 = 50^2, so r = 10
The right angle will be at the center of A if (20+r)^2 + 50^2 = (30+r)^2; so r = 100
If A and B are externally tangent to each other but internal to C, then if the right angle is at the center of C then, (r30)^2 +(r20)^2 = 50^2; so r = 60
Have to go now... leave the last case till later.

Posted by Charlie
on 20040527 16:01:05 