Online Geometry Problems, High School, College

Online Geometry Problem 445: Three Tangent Circles, Tangency Points, Circumradius

The figure shows three circles A,B, and C with radii 6, 2, and 4, respectively, each tangent to the other two at the points D, E, and F. Find the circumradius of triangle DEF.
The circumradius of a triangle DEF is the radius of a circle that passes through the vertices D, E, and F.
 

Three tangent circles, circumradius
 

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