Let ABCD be a tetrahedron. Denote by S1 the inscribed sphere inside it, which is tangent to all four faces. Denote by S2 the outer escribed sphere outside ABC, tangent to face ABC and to the planes containing faces ABD,ACD,BCD. Let K be the tangency point of S1 to the face ABC, and let L be the tangency point of S2 to the face ABC. Let T be the foot of the perpendicular from D to the face ABC.Prove that L,T,K lie on one line. geometry3D geometrytetrahedronsphere