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Tangent Circles

Submitted By:shenqiang
Fun:** (1.68)
Difficulty:** (2)

Four circles are situated in the plane so that each is tangent to the other three.

If three of the radii are 3, 4, and 5, what's the largest possible radius of the fourth circle?


The four circles can be tangent to each other at the same point, therefore there is no upper bound to the radius of the fourth circle!

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