Go Geometry Problem Problem 463: Three Concentric Circles, Secant, Tangent, Triangle, Area

Problem 463. The figure shows three concentric circles C1, C2, and C3, with center O. Line ABC is a secant to circles, OD is perpendicular to line ABC extended, line AEF is tangent to circle C1 at A, line BGF is tangent to circle C2 at B, and line CGE is tangent to circle C3 at C. If AB = a, BC = b, and OD = c, prove that the area of triangle EFG is Formula to prove.
 

Three concentric circles, secant, tangent, area
 

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