I would to like find the radius for the biggest circle which touches other three circle.Let me explain my problem in detail.

I have one bigger circle A with radius 15.

Inside this bigger circle i have another circle B with radius 3 which touch this bigger circle. Have another circle C with radius 4 which touches A and B. I would like to draw a biggest circle which touches A,B and C.

Your help in this regard will be highly appreciated.

Regards,
Ananth.

Ananth,

If you just want the radius r of the fourth circle, you can use Descartes' circle theorem. (See, for example, H.S.M. Coxeter, INTRODUCTION TO GEOMETRY, pages 13 to 15): r is the positive root of the quadratic equation

2(1/9 + 1/16 + 1/r² + 1/225) = (1/3 + 1/4 + 1/r - 1/15)².

You can look it up in many geometry texts under the name "the problem of Apollonius" or search the Internet for "the problem of Apollonius". Let me know if you'd like me to send you the recipe.

Chris