The figure shows a triangle ABC and a cevian BD. O1, O2, and O3 are
the incircles of triangles ABD, ABC, and BDC. If BE = 4, and BG =
5, find the measure of DF.
Incircle is a circle within a triangle, that is tangent to each side.
A cevian is any segment drawn from a vertex of a triangle to the opposite side or its extension.