Infographic Geometry Problem 918: Triangle, Incenter, Incircle, Angle Bisector, Perpendicular, Metric Relations. Level: High School, College, Mathematics Education

In a triangle ABC (figure below), I is the incenter and FD is perpendicular to CI. If AF = 9 and BD = 4, find DF.

Infographic Geometry Problem 918: Triangle, Incenter, Incircle, Angle Bisector, Perpendicular, Metric Relations