Problem

Source: Ukrainian TST for RMM 2021(2) and EGMO 2022 P3

Tags: geometry



$AL$ is internal bisector of scalene $\triangle ABC$ ($L \in BC$). $K$ is chosen on segment $AL$. Point $P$ lies on the same side with respect to line $BC$ as point $A$ such that $\angle BPL = \angle CKL$ and $\angle CPL = \angle BKL$. $M$ is midpoint of segment $KP$, and $D$ is foot of perpendicular from $K$ on $BC$. Prove that $\angle AMD = 180^\circ - |\angle ABC - \angle ACB|$. Proposed by Mykhailo Shtandenko and Fedir Yudin