Tangent-ing all around!
Geometry
Level
3
Find the radius of the circle (shown by dotted lines) circumscribing the three mutually tangent circles (in cm).
The answer is 15.31946787.
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1 solution
If the radii of the three inner circles are denoted by r, g and b
Then the Radius of the Outer Soddy circle is given by
-(r g b)/(r g + g b + b r - 2 sqrt(r g b*(r + g + b)))