MathDB
BD + BA = AC if <B=3<C, <BDC=2<C (2019 Novosibirsk Oral Geo Oly 7.5)

Source:

April 26, 2021
geometryequal angles

Problem Statement

Given a triangle ABCABC, in which the angle BB is three times the angle CC. On the side ACAC, point DD is chosen such that the angle BDCBDC is twice the angle CC. Prove that BD+BA=ACBD + BA = AC.