Problem

Source: - All-Russian MO 2003 Regional (R4) 11.7

Tags: geometry, angle bisector, 3D geometry, sphere, tetrahedron



Given a tetrahedron $ABCD.$ The sphere $\omega$ inscribed in it touches the face $ABC$ at point $T$. Sphere $\omega' $ touches face $ABC$ at point $T'$ and extensions of faces $ABD$, $BCD$, $CAD$. Prove that the lines $AT$ and $AT'$ are symmetric wrt bisector of angle $\angle BAC$