MathDB
Property of Orthocenter

Source: Turkey TST 2016 P1

April 10, 2016
geometry

Problem Statement

In an acute triangle ABCABC, a point PP is taken on the AA-altitude. Lines BPBP and CPCP intersect the sides ACAC and ABAB at points DD and EE, respectively. Tangents drawn from points DD and EE to the circumcircle of triangle BPCBPC are tangent to it at points KK and LL, respectively, which are in the interior of triangle ABCABC. Line KDKD intersects the circumcircle of triangle AKCAKC at point MM for the second time, and line LELE intersects the circumcircle of triangle ALBALB at point NN for the second time. Prove thatKDMD=LENE    Point P is the orthocenter of triangle ABC \frac{KD}{MD}=\frac{LE}{NE} \iff \text{Point P is the orthocenter of triangle ABC}