The three circles in the diagram above all are tangent to the line in the picture. The radius of circle A is a, of circle B is b, and of circle C is c. All three circles are tangent to each other. What is c as a function of a and b?
I have an answer that checks out on a couple of examples, but I don't know how to obfuscate it, except to say that it uses three of the four primary functions, and is both radical and square.
Sounds like it is probably right. I will wait for awhile to give others a chance to try it. Here is another one that is similar to keep you busy while you are waiting ;-)
The three colored circles in the diagram above have radii of 1, 2, and 3, and each are tangent to the other two. A fourth interior circle is tangent to all three colored circles. What is the radius of the interior circle? For extra credit what is the radius of the exterior circle (not pictured) that is tangent to the three colored circles?
Look at the lines connecting the centers of the circles. Their lengths are a+c, b+c, and a+b. The vertical components of those lines are a-c, b-c, and a-b. Pythagorus gives us the horizontal components of those lines, and noting that the horizontal distance between the centers of A and B is equal to the sum of the horizontal distances from A to C and C to B. it is easy to set up an algebraic expression leading to the answer above.