MathDB
<APB+ <MPC=180

Source: 2023 Viet Nam math olympiad for high school students D1 P3

March 25, 2023
geometry

Problem Statement

Given a triangle ABCABC isosceles at A.A. A point PP lying inside the triangle such that PBC=PCA\angle PBC=\angle PCA and let MM be the midpoint of BC.BC.
Prove that: APB+MPC=180.\angle APB+ \angle MPC =180^{\circ}.